Some time ago I misplaced one of the lens covers for my Tasco 30mm Red Dot sight. I searched for a replacement and found that they are very difficult to find - or you can pay $10-15 each for upgraded replacements with flip-up and see-through features (which I don't care for).

So - I made my own using the cap from an old prescription medicine bottle.

Tools & materials:

70 mm x 30 mm pill bottle
razor knife and a steady hand

Optional:

black paint
30 cm of paracord
drill and bit sized same diameter as the paracord
cigarette lighter

Step 1: Cut Carefully!

Inside the pill bottle lid are 5 small nubs that normally lock into guides on the bottle's body. Shave them off flush using the razor knife, leaving a round 38 mm inside diameter (ID) cap.

Actually you can stop here, the cap will now fit over the 38.5 mm outside diameter of the sight body.

Or - you can do a little more...

Step 2: A Little Bit of Aesthetic and Functional Improvement

I painted the cap black on the outside (not the inside as that would likely change the fit from "snug' to "impossible"!)

Then I drilled a hole in the bottle cap the same size as my paracord's diameter, inserted one end of the cord, and used a cigarette lighter to seal the end of the cord, which also effectively created a small hard plastic knot on the "inside" of the cap which prevents the cord from pulling back through.

I then did the same thing with the remaining original lens cap I still had so that the two caps are attached with about 30 cm of cord between them.

This setup serves two functions:

Keeps the caps from getting separated
Allows me to pull them off and leave the cord wrapped around the mounting base of the Red Dot sight where they won't get separated from the rifle and lost.