Picatinny rail (MIL-STD-1913): profile, grooves and mount jaw — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/picatinny-rail-mil-std-1913/  (sheet CC BY 4.0)
Basis: MIL-STD-1913 (AR), Figures 1 and 2 (public release)
Catalog version: 2026-10-20

Overall (mm): width 21.209, height 9.322
- MIL-STD-1913 is the Picatinny accessory rail: lights, lasers, optics, red dots, grips, bipods, cameras and phone mounts clamp across its 45° dovetail flanks, and a key in the clamp sits in a recoil groove so the accessory cannot slide.
- Every number here is from the standard's Figure 1 (profile) and Figure 2 (recoil groove), printed in inches; the mm values are exact conversions. The standard is public (Distribution Statement A).
- Groove dimensions apply to all grooves; the number of grooves depends on the application. Accessory makers often count rail length in slots: an n-slot section is n × .394 in long.
- The mount-jaw file is the female shape at nominal size with one recoil key: subtract or adapt it for your mount, and add your process clearance on the flanks (a printed clamp typically needs a few tenths of a mm).
- Weaver rails share the outer shape loosely but have narrower .180 in grooves without a fixed spacing: Weaver accessories usually fit Picatinny, Picatinny accessories often do not fit Weaver.

parameter  value
width across the 45° edges  .835 −.005 in (21.209 mm)
top flat (datum C)  .748 ±.002 in (18.999 mm)
neck width  .617 −.010 in (15.672 mm)
lower flank  45°, .108 in (2.743 mm) deep (basic)
upper edge  45° from the top flat to the widest point (1.105 mm)
top to neck  .164 −.020 in
rail height above the mounting surface  .367 in min (9.322 mm)
recoil groove width  .206 +.008/−0 in (5.232 mm)
recoil groove depth  .118 +.008/−0 in (2.997 mm)
groove spacing (centre to centre)  .394 in basic (10.008 mm)
edge break / fillets  .002 +.010 in / .020 ±.015 in

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- US Army ARDEC (via EverySpec): MIL-STD-1913 (AR): Dimensioning of accessory mounting rail for small arms weapons, 1995 (Distribution A, public release) — web — US Government work, public release — https://everyspec.com/MIL-STD/MIL-STD-1800-1999/MIL-STD-1913_17705/
- Wikipedia: Picatinny rail (Weaver compatibility) — web — Publisher's page; dimensions are facts — https://en.wikipedia.org/wiki/Picatinny_rail

Free files (CC BY 4.0, Xem Studio; STEP + STL, 6 parts): https://xemstudio.com/files/hardware/picatinny-rail-mil-std-1913/index.json
API: https://xemstudio.com/api/geometry?object=picatinny-rail-mil-std-1913