Well, the bad news first, it's a Craftsman and parts availability is, well, spotty, to be charitable. A once great brand reduced to pity.
It does look like you have a 1/2" collet but the picture could be deceiving. Is it damaged?
For some hope, many of the craftsman routers were made by other manufacturers and you might be able to figure out who made this one. Craftsman archaeology isn't my specialty but there are others that might be able to help. I'd try general routing or router reference subforums. Also, post the exact model number - it should be on a plate on the back of the motor. I'd also try googling the model number to see what pops up.
Unfortunately, Craftsman parts are very hard to come by. The brand just got bought out, so parts are even harder to find. Someone here mentioned there was a different brand with the same collet size, but I've lost track of the string.
Collets are actually very precise devices so the right thread size and count may or may not work on your Craftsman. Most of the time, you wind up having to buy a new router. If that happens, check out the Bosch 1617 EVSPK kit. Very highly regarded around here, and the kit comes with both fixed and plunge bases and will do for both freehand and table use.
Hopefully the member who posted the alternative brand collet will catch this thread and post.
I've come to learn that many router makers outsourced their collets. For example the collet on the Bosch 1617 is also used by 15 or so DeWalts and 3 models of Hitachi. An older DW I own appears to use an old Bosch WK series collet. You might try looking through Elaire's site to see if anything there appears the same as yours. If it looks the same then the chances are pretty good in my opinion that they are the same. Otherwise you'll need to find another router like yours that has good collets. https://elairecorp.com/
If the 1/2" collet is still good, they make reducer bushings to fit smaller bits into it, but make sure that you buy one of the better ones. It should have 3 segments and not just one split down one side. The cheaper don't hold bits well, and you don't want them moving or coming out at 20,000 + rpm.
Correct me if I'm wrong but wouldn't a type 4 Musclechuck work in this case? Don't you remove the existing chuck and install the MC in it's place. Of course the cost may be more than he has in the router.
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