In article , Stephen Mitchell
says...

Thorp used Monel pops .... a number of certificated aircraft also use Monel
pops.

Correct, proving the point that all rivets don't have to be the solid bucked
style as someone wrote. There's pop rivets and there's pop rivets just like
there's alum and there's alum. So just because some designers use pop rivets
does'nt mean their design is inferior to one that's using buck rivets.That's all
:-)

See ya

Chuck S