above: Sousa Necks and Bits - Allied Supply Catalog pg. 75
A while back a posted some photos of Sousaphone necks and bits with some additional information. If you want to revisit this, you can click on this link:
Above is a scan of page 75 from The Allied Supply Catalog. It has photos and tenon dimensions. This page can be helpful to help identify the parts you may have but don't know what they are or if you have mis-matched parts (wrong combination of neck and bits) or what parts you may need if you are missing something.
Conn bits are completely interchangeable with one another. King bits have to be in a certain order. 1 bit accepts the other and 1 bit accepts the mouthpiece. Other makers like Holton, Jupiter and Selmer have 1 bit that takes the mouthpiece and 1 bit that has a tension screw. I personally prefer the Conn bits (when you can use them) because they are freely interchangeable.
Either way, I think it's pretty neat to see all of them laid out.
IMPORTANT NOTE: Allied Supply is a wholesaler and you cannot purchase from them directly unless you are a repair outfit. If you need to order any neck or bits, contact me at Wichita Band Instrument Company and I can supply them for you, or visit your local repair shop.
Thanks to Craig Anderson at Allied Supply for granting permission to use this image!