This Baader Sliding T-2 Focuser is an adapter which functions as a variable length T-thread adapter as well as a T-thread to 1.25" eyepiece holder.
This Baader T2 focuser consists of two parts. The inner part has a female T-thread on one side and a 1.25" eyepiece holder/barrel with a single thumbscrew on the other. The total length of this part is 29 mm (1.14"). The outer portion of the assembly is an adapter that cannot be used alone, but slides over the inner part. This combination functions as a variable T-thread spacer with a male T-thread on one side and a female T-thread on the other. The total length of this combined adapter can be adjusted from 31.5 mm (1.24") to 42.5 mm (1.67").
The outer sliding sleeve clamps down on the inner adapter with another thumbscrew. (Realistically, this is not a conventional "focuser" in the normal sense as used by astronomers.) However, it is possible to use it as a focuser, if you slide the inner eyepiece holder manually until you achieve focus, then lock it in place.