1x30 red dot protection ring

This is a simple ring to fix cheap 30mm plexiglass discs to a cheap chinese 1x30 red dot sight frequently used in airsoft.

Just get some cheap 30mm plexiglass rings of ebay:
https://www.ebay.com/itm/Acrylic-Perspex-Disk-Circle-Clear-3mm-Thick-10mm-to-100mm-Diameter/292995580241

The cheap 1x30 red dot scope: http://s.click.aliexpress.com/e/KMwdvnVA

All in all you have a well protected airsoft scope for 15 bucks. If a disc gets shot out, just replace it.