TS Adaptor with T2 female thread and M48 (2" filter thread) male - zero effective length
... the adaptor is screwed onto a T2 male therad and converts it to the 2" filter thread.
Simply screw this conversion adaptor onto a male T2 thread to turn it into an M48 male thread. M48 is the standard thread used for 2" astronomical filters and is also present in many 2" adaptors.
The adaptor's extremely short length of only 2.5mm adds zero effective length to the setup as a whole - it is shorter than the average T2 male thread.
-- T2 female thread (M42x0,75)
-- M48x0.75 male thread (2" filter thread)
-- mechanical length only 2.5mm
TS Adaptor with T2 female thread and M48 (2" filter thread) male - zero effective length ..