Ø3" Lens Tubes

  • Directly Accepts Ø3" (Ø76.2 mm) Optics
  • Compatible with All SM3-Threaded Components
  • Stackable Design Enables Construction of Multi-Element Optical Systems











Easily Interface with Other Lens Tube Sizes

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Additional Lens Tube Sizes
Ø30 mm
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  • Easily Construct Multi-Element Optical Systems
  • Designed for Compatibility with Ø3" (Ø76.2 mm) Optics
  • Wide Range of SM3-Compatible Optomechanical Components Available

Lens tubes are ideal for creating compact optical subassemblies. The Ø3" lens tubes sold here can be used to house one or several optical elements. Optics are separated and secured by retaining rings that are positioned at the desired depth within the lens tube using a spanner wrench. These stackable lens tubes ship with one retaining ring. Additional retaining rings can be purchased separately. In addition to the Ø3" lens tubes featured on this page, Thorlabs also offers Ø1/2", Ø1", Ø30 mm, Ø1.5"Ø2", and Ø3" versions, each of which is equipped with an SM series thread standard that depends on the tube diameter.

For fine tuning of the first or last lens in a lens tube system, consider using a SM3V10 Adjustable Length Lens Tube.

Lens Tube Application Example
Lens Tube Compatible Products
Terminated Fiber
Fixed Fiber Collimator
Kinematic Fiber Collimator
LED Mounts LD Mounts Aspheric Lens Mounts Irises, Apertures, and Shutters Alignment Tools

Threading Specifications

The following is a general overview of screw threading. For more details regarding specifications and dimensions, please consult the Machinery's Handbook, available for purchase at many bookstores.

Features of a Thread
A thread consists of three repeating features: a crest, flank, and root (see drawing to the right). Except in special cases, threads have symmetrical sides inclined at equal angles when a vertical line is drawn through the center of a crest or root. The distance between corresponding points on adjacent threads is known as the pitch of the thread. The flank angle is defined as the angle the flank makes with a perpendicular ray drawn from the screw axis. Unless otherwise stated, threads have a flank angle of 30°, resulting in a total angle between flanks of 60°. Each feature is shown in the diagram to the right.

The major diameter is taken from the crests of a thread while the minor diameter is taken from the roots. For most screws, crests and roots do not terminate at a sharp point, so crest and root truncation values are included in the definitions of major and minor diameter. The pitch diameter is approximately halfway between the major and minor diameters.

Thread Form
A thread form is a set of rules that define the features' scale relative to one another. Common thread forms include the Unified Screw Thread Form, used in the United States of America and measured in imperial units, and the ISO Metric Screw Thread Form, used in many parts of the world and measured with the International System of Units. There are many thread forms in the Unified screw thread standard designated by either UN, which defines a flat root contour, or UNR, which defines a round root contour. These can be further described by appending more letters. For example, an extremely fine thread with a flat root contour is designated UNEF. Those forms which are not standardized by the Unified screw thread system are designated UNS.

Thread Series
Most screws are identified by their thread series. Thread series are denoted by the major diameter and density of threads. Unified threads specify density in threads per inch, while Metric threads specify the thread pitch. For example, in the Unified nomenclature, a 1/4"-20 cap screw has a 1/4" diameter barrel and the pitch is 20 threads per inch (TPI). In metric nomenclature, an M4 x 0.7 cap screw has a 4 mm barrel and the pitch is 1 thread per 0.7 mm. The term M4 x 0.7 is often shortened to just M4.

Unified Thread Class Tolerancing
Location Loose Optimal Strict
Internal 1B 2B 3B
External 1A 2A 3A
Metric Thread Tolerance Positions
Location Loose Optimal Strict
Internal - G H
External e or f g h
Metric Thread Tolerance Grades
Dimension Location Tolerance Gradesa
Minor Diameter Internal 4, 5, 6, 7, 8
Major Diameter External 4, 6, 8
Pitch Diameter Internal 4, 5, 6, 7, 8
External 3, 4, 5, 6, 7, 8, 9
  • The tolerance becomes looser as the grade increases. The underlined grades are used with normal lengths of thread engagement.

Thread Class
The tolerances and allowances on a thread series are given by a thread class. Unified thread classes are alphanumeric identifiers starting with a number from 1 through 3, where 1 is the loosest tolerance and 3 is the tightest, and either A for external threading or B for internal threading.

Metric threads have a slightly more complex tolerancing method that uses tolerancing grades, designated by a number 3 through 9; and tolerancing positions, which use letters e through h. Grades provide a measure of the tolerance itself: the smaller the number, the tighter the tolerance. Positions denote the distance of the tolerance from the pitch diameter. Uppercase positioning letters indicate internal threads while lowercase positioning letters indicate external threads.

Quoting from the Machinery's Handbook, 29th Edition, p. 1885: "To designate the tolerance class, the grade and position of the pitch diameter is shown first followed by that for the major diameter in the case of the external thread or that for the minor diameter in the case of the internal thread, thus 4g6g for an external thread and 5H6H for an internal thread. If the two grades and positions are identical, it is not necessary to repeat the symbols, thus 4g, alone, stands for 4g4g and 5H, alone, stands for 5H5H."

Thorlabs' SM Series Threads
Threading specifications for our SM threads, utilized in our lens tube and cage system components, are given below so that you can machine mating components to suit your application. Most SM series threads utilize a non-standard Unified thread form, indicated by the letters UNS, with a 30° flank angle and a thread class of 2A and 2B. The exception is our SM30 series thread, which is a Metric thread form with a 30° flank angle and a tolerance of 6H/6g. We also offer products with C-Mount and RMS threads, and the specifications for these threads are given below for reference. Please note that other manufacturers may have different tolerances for C-Mount and RMS threads. For other thread specifications that are not listed here, please contact Tech Support.

SM05 Threading: Ø1/2" Lens Tubes, 16 mm Cage Systems
External Thread, 0.535"-40.0 UNS-2A Internal Thread, 0.535"-40.0 UNS-2B
Max Major Diameter 0.5340" Min Major Diameter 0.5350"
Min Major Diameter 0.5289" Min Pitch Diameter 0.5188"
Max Pitch Diameter 0.5178" Max Pitch Diameter 0.5230"
Min Pitch Diameter 0.5146" Min Minor Diameter (and 83.3% of Thread) 0.508"
Max Minor Diameter 0.5069" Max Minor Diameter (and 64.9% of Thread) 0.514"
RMS Threading: Objective, Scan, and Tube Lenses
External Thread, 0.800"-36.0 UNS-2A Internal Thread, 0.800"-36.0 UNS-2B
Max Major Diameter 0.7989" Min Major Diameter 0.8000"
Min Major Diameter 0.7934" Min Pitch Diameter 0.7820"
Max Pitch Diameter 0.7809" Max Pitch Diameter 0.7866"
Min Pitch Diameter 0.7774" Min Minor Diameter (and 83.3% of Thread) 0.770"
Max Minor Diameter 0.7688" Max Minor Diameter (and 64.9% of Thread) 0.777"
C-Mount Threading: Machine Vision Lenses, CCD/CMOS Cameras
External Thread, 1.000"-32.0 UN-2A Internal Thread, 1.000"-32.0 UN-2B
Max Major Diameter 0.9989" Min Major Diameter 1.0000"
Min Major Diameter 0.9929" Min Pitch Diameter 0.9797"
Max Pitch Diameter 0.9786" Max Pitch Diameter 0.9846"
Min Pitch Diameter 0.9748" Min Minor Diameter (and 83.3% of Thread) 0.966"
Max Minor Diameter 0.9651" Max Minor Diameter (and 64.9% of Thread) 0.974"
SM1 Threading: Ø1" Lens Tubes, 30 mm Cage Systems
External Thread, 1.035"-40.0 UNS-2A Internal Thread, 1.035"-40.0 UNS-2B
Max Major Diameter 1.0339" Min Major Diameter 1.0350"
Min Major Diameter 1.0288" Min Pitch Diameter 1.0188"
Max Pitch Diameter 1.0177" Max Pitch Diameter 1.0234"
Min Pitch Diameter 1.0142" Min Minor Diameter (and 83.3% of Thread) 1.008"
Max Minor Diameter 1.0068" Max Minor Diameter (and 64.9% of Thread) 1.014"
SM30 Threading: Ø30 mm Lens Tubes
External Thread, M30.5 x 0.5 – 6H/6g Internal Thread, M30.5 x 0.5 – 6H/6g
Max Major Diameter 30.480 mm Min Major Diameter 30.500 mm
Min Major Diameter 30.371 mm Min Pitch Diameter 30.175 mm
Max Pitch Diameter 30.155 mm Max Pitch Diameter 30.302 mm
Min Pitch Diameter 30.059 mm Min Minor Diameter (and 83.3% of Thread) 29.959 mm
Max Minor Diameter 29.938 mm Max Minor Diameter (and 64.9% of Thread) 30.094 mm
SM1.5 Threading: Ø1.5" Lens Tubes
External Thread, 1.535"-40 UNS-2A Internal Thread, 1.535"-40 UNS-2B
Max Major Diameter 1.5339" Min Major Diameter 1.535"
Min Major Diameter 1.5288" Min Pitch Diameter 1.5188"
Max Pitch Diameter 1.5177" Max Pitch Diameter 1.5236"
Min Pitch Diameter 1.5140" Min Minor Diameter (and 83.3% of Thread) 1.508"
Max Minor Diameter 1.5068" Max Minor Diameter (and 64.9% of Thread) 1.514"
SM2 Threading: Ø2" Lens Tubes, 60 mm Cage Systems
External Thread, 2.035"-40.0 UNS-2A Internal Thread, 2.035"-40.0 UNS-2B
Max Major Diameter 2.0338" Min Major Diameter 2.0350"
Min Major Diameter 2.0287" Min Pitch Diameter 2.0188"
Max Pitch Diameter 2.0176" Max Pitch Diameter 2.0239"
Min Pitch Diameter 2.0137" Min Minor Diameter (and 83.3% of Thread) 2.008"
Max Minor Diameter 2.0067" Max Minor Diameter (and 64.9% of Thread) 2.014"
SM3 Threading: Ø3" Lens Tubes
External Thread, 3.035"-40.0 UNS-2A Internal Thread, 3.035"-40.0 UNS-2B
Max Major Diameter 3.0337" Min Major Diameter 3.0350"
Min Major Diameter 3.0286" Min Pitch Diameter 3.0188"
Max Pitch Diameter 3.0175" Max Pitch Diameter 3.0242"
Min Pitch Diameter 3.0133" Min Minor Diameter (and 83.3% of Thread) 3.008"
Max Minor Diameter 3.0066" Max Minor Diameter (and 64.9% of Thread) 3.014"
SM4 Threading: Ø4" Lens Tubes
External Thread, 4.035"-40 UNS-2A Internal Thread, 4.035"-40.0 UNS-2B
Max Major Diameter 4.0337" Min Major Diameter 4.0350"
Min Major Diameter 4.0286" Min Pitch Diameter 4.0188"
Max Pitch Diameter 4.0175" Max Pitch Diameter 4.0245"
Min Pitch Diameter 4.0131" Min Minor Diameter (and 83.3% of Thread) 4.008"
Max Minor Diameter 4.0066" Max Minor Diameter (and 64.9% of Thread) 4.014"

Posted Comments:
Philipp K  (posted 2020-12-15 06:56:17.1)
Hi, would you also do a 4" lens tube (plus retaining ring and 3" adaptor) as a custom version? thanks and best, Philipp
YLohia  (posted 2020-12-15 02:35:27.0)
Hello Phillip, custom versions of these lens tubes can be requested by emailing your local Thorlabs Tech Support team (in your case, europe@thorlabs.com). We will discuss this further directly.
John Baxley  (posted 2020-10-08 14:12:31.223)
Brandon is patent and knowledgeable. He deciphered what I want and led me right to it. I am right now making his suggestions part of my design in CAD. Give Brandon more money! Thank you for your valuable time, John Baxley LUNA Atlanta FYI: Seems if you mess up the security code the feedback page just blanks (it does not return you back to all that you just typed but instead just blanks all entries. God knows how much feedback you have lost from that...
YLohia  (posted 2020-10-09 04:57:59.0)
Hello John, thank you for your feedback! We're always happy to hear about the performance of our applications engineers and are glad that Brandon was able to help you out with your problems. We are looking into the issue regarding the security code on the form.
howardbourne  (posted 2015-03-24 19:44:02.953)
Hi there, I would also like to buy several 6" SM3 series tubes. When will these be available?
cdaly  (posted 2015-03-25 03:31:17.0)
Response from Chris at Thorlabs: There are no plans to release a 6" version of the SM3 lens tube at this time, but this may change if it seems to be a commonly requested item. For the time being, we should be able to offer them as custom items. I will contact you directly about this.
iain  (posted 2014-11-27 14:03:03.187)
Could you give the lengths of the SM3L05, SM3L10 and SM3L20 lens tubes in millimetres as well as inches? Do you make a 76.2 mm (3 inch) long SM3 lens tube?
cdaly  (posted 2014-12-02 03:50:35.0)
Response from Chris at Thorlabs: Both the imperial dimensions and metric equivalents can be found on the technical drawing for any parts. This can be found by clicking on the red icon next to the part number, under where it says DOCS, and then choosing the AutoCAD PDF option. In these cases, the metric lengths are 12.7mm, 25.4mm, and 50.8mm respectively. At this time, we do not offer a 3"(76.2mm) version as a stock item, though the 1" and 2" version can be stacked.
user  (posted 2011-11-30 10:00:59.0)
A response from Tyler at Thorlabs: Hello Ed, Thank you for suggesting that we add longer 3 inch diameter lens tubes. Are there any other 3 inch diameter lens tube products that you need?
ed  (posted 2011-11-29 11:18:12.0)
I hope you are planning on extending the SM3 tube series to 3" long and a 6" long like you have for the SM2 series.
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Ø3" Stackable Lens Tubes

SM3Lxx Lens Tube Diagram
  • SM3-Threaded (3.035"-40) Bore Directly Accepts Ø3" (Ø76.2 mm) Optics
  • Stackable Design Enables Multi-Element Optical Systems
  • Ideal for Large Optical Assemblies

These stackable Ø3" lens tubes provide a fast and easy means for building compact optical assemblies. Their stackable design and direct interfacing with any SM3-threaded (3.035"-40) components provide flexibility for complex optomechanical assemblies. One SM3RR retaining ring is included with each lens tube.

Item # L Internal Thread Depth
SM3L05 0.53" (13.5 mm) 0.50" (12.7 mm)
SM3L10 1.03" (26.2 mm) 1.00" (25.4 mm)
SM3L20 2.03" (51.6 mm) 2.00" (50.8 mm)
Alternatives Ø1/2", Ø1", Ø30 mmØ1.5", and Ø2" Stackable Lens Tubes Ø1" and Ø2" Lens Tube Extensions Ø1" and Ø2" Lens Tubes with Side Access Ports
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
SM3L05 Support Documentation
SM3L05SM3 Lens Tube, 0.5" Thread Depth, One Retaining Ring Included
SM3L10 Support Documentation
SM3L10SM3 Lens Tube, 1" Thread Depth, One Retaining Ring Included
SM3L20 Support Documentation
SM3L20SM3 Lens Tube, 2" Thread Depth, One Retaining Ring Included
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Ø3" Retaining Rings and Spanner Wrenches

  • SM3RR Retaining Rings Secure Ø3" (Ø76.2 mm) Optics
  • Spanner Wrenches Provide One-Handed Adjustment of SM3RR Retaining Rings
  • SPW801 Adjustable Spanner Wrench can Accommodate Diameters from 0.12" (3.0 mm) to 2.89" (73.4 mm)

Due to its hollow design, the SPW605 Spanner Wrench enables retaining rings for our SM3 series of lens tubes to be adjusted and installed without obscuring the beam path. The handle is knurled for improved grip. Alternatively, the SPW801 Adjustable Spanner Wrench can also be used to position SM3RR retaining rings. Please note that the SPW801 wrench can withstand a maximum torque of 80 inch pounds. We also offer the SPB3 Spanner Bit, which can be used with a standard 1/4" hex driver (sold separately). The SPB3 is included as part of the SPB600 Spanner Wrench Bit Kit.

Alternatives Ø1/2", Ø1", and Ø2" Fixed Diameter Spanner Wrenches Ø1/2", Ø1", Ø1.5", and Ø2" Retaining Rings
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
SM3RR Support Documentation
SM3RRSM3 Retaining Ring for Ø3" Lens Tubes and Mounts
SPW605 Support Documentation
SPW605Spanner Wrench for SM3-Threaded Retaining Rings, Length = 4.35"
SPW801 Support Documentation
SPW801Adjustable Spanner Wrench
SPW102 Support Documentation
SPW102Adjustable Spanner Wrench, Replacement Blade Set