If it meets NACM specifications for chain thickness in-use, plus and acceptable allowance for wear for the next few years. You will need to measure both the thickness of the links (after removing all rust) at the link ends, where they bear, and the length of the links.
It is all in the specification, which you can easily Google and download.
- Excessive wear. If the wear on any portion of any link exceeds the allowable wear shown on this* table remove from service.
* Chain Wear ➥ https://www.peerlesschain.com/technical-info/#4
- Twisted, bent or cut links.
- Cracks in the weld area or any portion of the link.
- Nicks or gouges.
- Stretched links.
- Severe corrosion.
- Any deformation or degradation of components.
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Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"