The standard right angle finder on the GSO 8" inch dob I'm preparing for my nephew didn't come with any end caps. Do you have any spare?
57.5mm cap for the objective (I assume that's what the 575 imprint is inside the caps I have on my own finders.. and I measure 25mm across the eyepiece end of the finder.
These can break and fall apart - I know Agena Astro has a range that would like to suit - https://astronomyconnect.com/items/c...ers/bnq?page=2 if that helps (realise postage as well). Wish I had a spare to give you.