The SM1A17 thread-to-thread adapter contains an internal M27 x 0.75 thread and an external SM1 (1.035"-40) 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 mount an objective to an SM1 lens tube. The unpackaged weight of this adapter is 3.18 g.