They're the same machine; the K (Kilbowie) was made in Great Britain (Scotland) and the W was made in the US (Bridgeport, Connecticut). The "W" stands for Wheeler & Wilson, the sewing machine company that Singer bought out circa 1905.

James

Oooh thank you Manalto! It's much longer than I thought! At least now I know what to look for. Does it go in the hole I saw through the slot? Mine has a set screw in there now and I am wondering it that should be removed!

You can call me James.

I wish I had a nickel... oh, never mind.

Inside the slot is a small raised area with a threaded hole. I'm assuming that's where someone has put a set screw. Since there is no other screw visible inside the slot, I think you're safe in removing it and replacing it with the proper screw. Did you find one in your bag of extras?

Ha! I knew that was a poor choice of words as soon as I posted it!

OK I took a photo of what I am seeing. You can see the threaded hole is open in the back but the hole inside the slot has a sew screw I think. I tried to remove it but I am going to have to use some penetrating oil to get it loosened first. I wonder if the set screw belongs in the hole in back then?

According to two of my 306es, the threaded hole at the back is open. The bight control screw goes where the set screw now resides. Penetrating oil should help; after it soaks for a day or two, try heating it up with a blow dryer when you attempt to remove it. Are you sure that's a set screw? Could it be the bight screw snapped off?

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:( It's looking that way. I tried cleaning it and finding a slot and it does look like it could be snapped off.

Someone who knows what s/he is doing can drill down the center of the snapped-off screw. It will collapse and can be removed. It's delicate work but can be done.

The fact that the screw snapped off indicates that the mechanism may be seized. Penetrating oil and heat should do the trick. Before you go through all this bother, decide if you think you'll ever need this function.

I think before I venture further with this I will clean the machine up and have it running. I agree that if it isn't something I would use there is no reason to take that risk.

I wonder about it being seized. Everything else on the machine seems to move very freely but maybe that's why they sold it!

That is exactly what is missing from my machine. Now I have to dig it out then dig through the screw drawer and see if anything matches. If not then what??? I'll have to see if the screw is broken off, too. Mine is mocha.

What exactly does that screw do?

It locks in a minimum stitch width if you want to toggle between two widths when doing decorative stitches. Without it, you still have all the decorative zigzag stitches and needle positions.

Translation: It's not important.