|When I bought Carriden in 2005 I found a similar issue with the tang for the lower shrouds on one side of the mast. However, on my mast the rivets are there essentially as a backup, since the tang and spreader cup assemblies are primarily held in place by a 3/8-inch or larger stainless steel bolt which goes right through the mast. The bolt is hidden inside the spreader cups and is not visible when the spreaders are in place. My conjecture is that the rivets are in place to help distribute the downward pull on the tang and thereby prevent the hole for the stainless bolt from elongating under load and wear. The original rivets appeared to be of stainless steel. I drilled out all of the rivets and replaced them with new stainless steel ones. Had to buy a whopping big commercial-grade pop riveter in order to fasten them in place. After eight seasons, there has been no visible fatigue or degradation, albeit in a fresh-water environment.
I have no idea about your rivets on the front of the mast. Where exactly are they located? My mast has no inner extrusions whatsoever. I had to install vinyl tubes and anchor them to the inside of the mast in order to protect my wiring from halyard chafe. I did use pop rivets when anchoring the tubes, but only in a few spots and they are all hidden under other fixtures. Between the anchoring method and the way in which the halyards have been led, it is virtually impossible for the lines to chafe on the rivets.
Marcus from Carriden
Mk III, Hull #847