Padeyes are great for mounting blocks and are also used as attachment points for staysails, reefing blocks, and hundreds of other items.
Harken offers a range of stainless steel padeyes. The diamond-shaped padeyes, 688 and 689, are 316 stainless and often used at mastbases where the diamond shape allows them to be mounted very close together. The 2759 is 316 cast stainless steel. The 627, 629, and 648 padeyes are 17-4 PH stainless.