In its basic configuration, the Barlow lens is ready for connection to 1.25" focusers and accepts 1.25" eyepieces.
If you have no problem with parts protruding into the drawer, for example when using refractors, the Barlow lens can simply be inserted into a 2" focuser, the reducer # 15 then serves as a 2" barrel.
Without thread protection ring, the reducer provides a T2 connection for cameras.
If you remove the reducer # 15 from the basic configuration, you can screw the Barlow into the filter thread of a 2" eyepiece; if you leave out the adapter # 29 as well, you get back to T2 for cameras.
If you unscrew the two rings # 25A and the adapter # 29 from the basic configuration, you can screw the adapter # 14 with built-in Barlow element into the reducer # 15 and then insert the Barlow lens into 2" focusers without protruding far into it. Photographically, after removing the thread protection ring, the rings # 25A can then be screwed onto the T2 thread of the reducer # 15, giving more distance again.
If you put the linked adapter TST2-2 on the previous arrangement, you can use 2" eyepieces, alternatively you can use adapter # 29 if you want to use only one single eyepiece.