I made some accessories for the Celestron FirstScope 76/300mm tabletop dobsonian. This scope is sold under different names, so if yours looks like the FirstScope or has a 90mm dust cap ring it'll probably fit too.

The primary reason for these caps is to step down the focal ratio for bright objects or long exposures, to reduce the coma caused by the edges of the mirror. By stepping down the aperture the image gets less bright but also sharper. Can be used for astrophotography or visual viewing of bright objects in daytime or the moon.

The bahtinov mask can be used for focussing on a bright star. And the blank/dust cap can be used to remix some other pattern onto it if you want to use it as a base.