I get asked these questions a lot, so I thought I would start a thread that I could reference, and a place where others could post related comments.
Saw chains are made up of cutters, drive links, and tie straps, and are held together by rivets. Since handling the tiny rivets could be awkward, pairs of rivets are pre-assembled to one tie strap ('preset' or 'pre-set') for use in joining chain to make loops, repairs, etc.
Preset and tie strap
Since each rivet also functions as a bearing, the center ('flange bearing' in illustration above) is harder, and a larger diameter than the 'hubs', which are spun down (or mushroomed with a hammer) to hold the chain together.
A spinner / breaker set is the preferred way to remove and install chain parts, although, there are some 'field expedient' methods for doing this with more basic tools.
https://www.arboristsite.com/community/threads/baileys-chain-breaker-and-spinner.144859/
https://www.arboristsite.com/community/threads/spinning-chain-fess-up.170216/
Philbert
Saw chains are made up of cutters, drive links, and tie straps, and are held together by rivets. Since handling the tiny rivets could be awkward, pairs of rivets are pre-assembled to one tie strap ('preset' or 'pre-set') for use in joining chain to make loops, repairs, etc.
Preset and tie strap
Since each rivet also functions as a bearing, the center ('flange bearing' in illustration above) is harder, and a larger diameter than the 'hubs', which are spun down (or mushroomed with a hammer) to hold the chain together.
A spinner / breaker set is the preferred way to remove and install chain parts, although, there are some 'field expedient' methods for doing this with more basic tools.
https://www.arboristsite.com/community/threads/baileys-chain-breaker-and-spinner.144859/
https://www.arboristsite.com/community/threads/spinning-chain-fess-up.170216/
Philbert