[Cherryville Chuck]

I looked here (https://www.ereplacementparts.com/craftsman-31517370-router-parts-c-158286_170726_170863.html) for the part but nothing looked like it and no diagram. I'm not sure what it does. There are very few critical parts for old Sears routers. The 315. means it was made by Ryobi but that probably won't help.

 

[Cherryville Chuck]

One thing to remember before spending money repairing a Sears router is that it will only be worth about $20 even if it runs. And if you need a collet for it there probably isn't one available anywhere. We probably get a dozen people a year looking for them and they have exhausted every other possibility already in many cases.