uxcell 20pcs M4 x 15mm Male Thread Knurled Knobs, Thumb Screws Clamping Knobs Grip 14mm Plastic Round Head Hand Knobs Thumbscrews, Black

I own a telescope and the parts that keep the lenses in place have small thumb screws that like to fall out sometimes. After losing one out in the middle of the desert one night, I started looking around for something with a larger knob so that it's easier to handle and I can see it if it falls out. These screws are ideal for my telescope. They are compatible with the old screws (which are standard on most telescopes), and fit perfectly. They make tightening the lenses down easier than the original screws.

I use these inconjuction with 3d printed parts. Works perfectly for this use.

I used these with threaded magnets. Turned out great. I also used threadlock to secure the threads.