I believe that Lark is the "New Royal" class made by free - so it takes a different shuttle than "regular" style Free machines.
These are the two I have of that class - and I've got lots of extra shuttles. Boye #19 -older ones take needle # 24 while newer ones take #16. On the Boye case it says "New Royal Old Style" and "New Royal Latest", however the case is from around 1910 -1920 . . My oldest case only has "New Royal" listed.
