I got tired of using tools to collimate my SCT, so I searched screw suppliers until I found one that carried a knob style thumbscrew that was the right size and length. I had to order a dozen screws as a minimum and I only have 2 8-inch Celestron C8 SCT's. I sold one set already, but still have one set of three for $10 including shipping.
These are the size that fits my celestron C8. I have two different OTA's, one is fastar compatible and the other is the non-fastar black tube that is just about four years old. They should work in any tube that uses a 6-32 x 5/16" or 6-32 x 3/8" collimation screw. But I have no idea if any tube besides the C8 uses this size. On the last ad I got lots of responses from people with larger Celestrons or Meade scopes, since none of them ever responded back after I told them to verify the size of the screw, I am guessing these will only fit the C8.
The screws are solid brass and have a knurled raised knod that makes collimation easy. I love mine. And yes they do still fit under the plastic lens cover. They are only about 3/8" tall. I will include a picture of them below.
(Wayne Augenstein, you didn't include your email, so I can't respond. Sorry.)