ISO a full lettera 22 mainspring in the housing. Pretty sure the one in the 1956 machine I am trying to get working again is broken and I am unsuccessful at getting the housing open, pretty sure I have bent the locking tab too far back and it won't go back in eventually even if I were able to fix the spring itself a la Phoenix Typewriter videos. Know your limits! It also seems to me that my (similarly broken) Studio 44 mainspring is the same size, just has a longer bolt...but maybe if I got an L32 parts machine I could scavenge the mainspring and it would fit perfectly, while also having a decade more life in it? Thanks all.