HI EMT and Sometimewoodworker. I bought a whole lot of different thumb screws to replace grub screws on some old hand routers. I got them, I think from Orbital fasteners, but because of the cost of postage I bought loads of different sizes of screws of every type and have a box of them in my garage.
If you can wait 3 weeks I'll post you one when i get back from holiday. They look like this. I think i have M4 to M8. Thumb screws do press into your fingers a bit, but these simple spade like ones work quite well. I'm back on 26th August and can send you, if its M4. But you will have to wait.
Thanks Tom
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