This is the cap that's used on the Tascam tension arms, this now is a very very rare part and everyone is after them as they always get lost, I bought a machine just to get some bits for me and these were spare.
These are rare now and TASCAM no longer offer them as a spare.
Many times people buy the wrong part then return it to me, this is the part you need on the moving tension arms on the far left and right of the machine.
PLEASE BE CAREFUL WITH THIS
The caps have a different longer thread to them the TSR8 cap is a straighter side but fits the 38 and vice versa e 38 cap has a bevel the TSR8 is straight a photo is included so you can see the difference. this listing is for the straight cap
the 32-34 etc 22-2 X series caps look correct from the front but they will not fit
please look at extra photos
it seems only on the 38 and TSR 8, you need teflon washers here on these