Vivitar Code Numbers
2X-xx   2x teleconverter 1   Pentax screw M42
3X-xx     3x teleconverter 2   Exakta / Topcon
TA-xx   T mount adapter 3   Nikon
AT-xx   Auto Extension Tube set 4   Canon FL, FD
5   Minolta MC, MD
6   Miranda  (early, w/ext release button)
(example:  2X-10 = Leicaflex 2X teleconverter) 7   Konica Autoreflex
8   Pentax screw M42,  Pentax ES, SP-F
9   Miranda  (late, EE function)
10   Leicaflex
11   Leica Thread, M39, LTM
12   Olympus Pen F, FT
Instituted when Vivitar was 13   Alpa
imported by Ponder & Best, 14   C mount
this numbering system was 15   Topcon RE super, Super D
abandoned early to mid 80's, 16   Zeiss contarex
prior to the introduction of 17   Topcon Uni, Auto 100, RE Auto
most autofocus mounts. 18   Zeiss Icarex bayonet
19   Retina Reflex, (Bessamatic?)
20     ? 
21   Olympus OM
22   Pentax K
23   Pentax Screw M42, Fujica ST 801, 901
24   Contax/Yashica
Note: MC  = Multi Coated