The SM1A28 thread-to-thread adapter contains an internal SM1 (1.035"-40) thread and an external M26 x 0.706 thread. Made of anodized aluminum, it is machined with the two threads connected by a flange and can be placed at the end of a threaded tube. It is typically used to create an objective from an SM1 lens tube. The unpackaged weight of this adapter is 2.49 g.