Pics of closed end water proof pop rivets, we purchased 5/32 closed end pop rivets with neoprene washers and 3/16 closed end pop rivets; the 5/32 use a washer and 3/16 are a cup head design no washer needed, 100 = $25 approx.
Notice the nail head is not showing on end shot
The 5/32 stainless with stainless mandrel showing the 3/16 is aluminium with steel mandrel. most rivets on the boler
are the 3/16 aluminium we got two lengths the shorter ones 19.95 a 100 and the longer ones 24.00 per 100
hope this helps
P.S. also got stainless backup washers for the rivets