Update 5/5/2019 - Added "Universal" flashlight mount, and Picatinny rail adapter. Also fine-tuned the hex nut hole and block size for better fit.

P365_AccessoryRail_Flash-i1R-EOS (Original)
This is a flashlight mount for the Sig Sauer P365's proprietary accessory rail. It is designed specifically for the Olight i1R EOS LED keychain flashlight, which is small enough to be practical for the P365. This mount grips the flashlight on only the back half, so the front half can be rotated for dim/bright/off settings. Also, the front half can be screwed off to access the built-in USB connector for recharging the battery without removing the flashlight.

P365_AccessoryRail_Universal
A generic mount, for many sizes of flashlights and laser pointers. Useful for testing options. Mount the flashlight with plastic cable ties through the rectangular holes provided in the mount.

P365_AccessoryRail_Picatinny
An adapter from the P365's proprietary rail, to a standard Picatinny rail. Useful for mounting many standard options. I've tuned the rail's slot positions so that a MantisX training sensor mounts backwards on the rail, tight against the trigger guard, leaving the charge port accessible from the front. For extra recoil strength, you may want to print this item vertically, with the front end flat on the printer table. See comparison photos above. Supports needed in either orientation.

All Mounts
For all parts, two halves (Left and Right) must be printed, then mounted using a 2.5mm (M2.5) socket-head cap screw and nut. Cap screw lengths needed:

• Flashlight Mounts: 16mm
• Picatinny Adapter: 12mm

The screw and nut are not generally available at hardware stores, but you should be able to get them from a hobby store (like a model RC store for model cars and planes) - for example, Du-Bro SKU 2119 and SKU 2104, or various M2.5 assortments from Amazon.