What type of stainless for chainplate bolts?

[jimgolding]

I have two chainplates that were mounted with carriage bolts, bolts in which the head is smooth and round and a short portion of the shank just below the head is square. To accept these bolts, the chainplates have square holes punched in them. Apparently these types of chainplates are susceptible to cracking at the corners of the square holes.

Anyway, one of my 20+ year old chainplates did have a crack and I'm getting new ones made with round holes. So, I'll be getting hex bolts to replace the carriage bolts.

Does anyone have input on the appropriate type of stainless steel (18-8, 316, etc.) for chainplate bolts? I'm in Florida, if that matters.

Thanks in advance.

Jim