Bart is correct, the variations in form (such as tail-taper, head thickness, length of threading) among same-size models is due to their being manufactured by different contractors. For example, there were several contractors making these fuzes in the Richmond vicinity.
Some differences in head-thickness and tail-taper are attributable to the late-war necessity of conserving copper. A clear example of that is the very-distinctive Atlanta Campaign version of roundshell Case-Shot fuzeplug with a steeply tapered tail.
Other differences are due to the fuzeplug's specific "application." Most of the long-model ones (for use in rifled-cannon shells) have a large-diameter hole in their base. Others have just a "pinhole" there because they were made for use in Case-Shot projectiles.
The great majority of these CS timefuze adapter-plugs have threading which is about .98" in diameter. But a few were made to fit a smaller or larger fuzehole, such as a British-made Whitworth shell's fuzehole, and a captured yankee Parrott shell's fuzehole.
Also, there are several "threading" variations. The vast majority are 12-threads-per-inch. But a few were made with a different thread pattern to fit non-CS-made shells, such as imported Britten shells )left-twist, 14-threads-per-inch) and captured yankee Schenkl shells (10 threads-per-inch).
Regards,
Pete
