OEM, not aftermarket. Conn & King, 5/16-24 thread, 5/32 bottom shoulder, lacquer or silver-plate bell screw. Contact us if you have questions on your model's fit. See my item ID# 16376 and 16377 for a slightly different aftermarket bell screw.
Fits:
14K Conn Sousaphone
2370 King Sousaphone
2341 King Tuba
2360 King Sousaphone
36K Conn Sousaphone
2341 (Old Detachable Bell Version) King Tuba
B1111 King Sousaphone
1529 King Sousaphone
2350 Body Lacquer King Sousaphone