Fiber Optics

https://dawsonprecision.com/fiber-optic-replacement-insert-6-or-12-red-or-green-by-dawson-precision/

https://www.amazon.com/TRUGLO-High-Visibility-Replacement-Firearm-Archery/dp/B004Z5BVG8?th=1

SA Ronin EMP: 0.060" diameter