Stellarvue 8 mm - 12 mm Variable Length M42 Extension Tube

Stellarvue 42 mm Variable Length Extension Tube This is an adjustable 42 mm extension tube that adds 8-12 mm of length. Thread is the standard 1.8" filter thread size of M42 X .75. The depth of the male thread is 8.3 mm and there is a thin (1.72 mm) threaded locking ring on this thread to adjust the spacing. The female thread is 5 mm deep. The body is 1.8" in outside diameter. The versatility of this adjustable spacer means you can tweak the focal distance when using different types of equipment in your optical chain, such as a focal reducer or off-axis guider.