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Picatinny rail (MIL-STD-1913): profile, grooves and mount jaw

Name: Picatinny rail (MIL-STD-1913): profile, grooves and mount jaw dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

What are the exact Picatinny rail dimensions (MIL-STD-1913)? · Standard part · basis: MIL-STD-1913 (AR), Figures 1 and 2 (public release)

Also called: picatinny rail dimensions, mil-std-1913, 1913 rail, picatinny slot width, picatinny slot spacing, picatinny rail stl, picatinny rail profile, picatinny mount design, 20mm rail, airsoft rail dimensions, weaver vs picatinny

Exact dimensions. True size, with no printing tolerance added.

width: 21.209 mm
height: 9.322 mm

Notes

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.

Picatinny rail (MIL-STD-1913): profile, grooves and mount jaw size chart

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

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

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
Wikipedia	Picatinny rail (Weaver compatibility)	web	Publisher's page; dimensions are facts

Free files

★ Free files 6 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

picatinny-rail-3-slot	3-slot rail section, 30.02 mm long (3 x .394 in), MIL-STD-1913 profile and grooves, true size	STEP · STL
picatinny-rail-5-slot	5-slot rail section, 50.04 mm long (5 x .394 in), MIL-STD-1913 profile and grooves, true size	STEP · STL
picatinny-rail-7-slot	7-slot rail section, 70.05 mm long (7 x .394 in), MIL-STD-1913 profile and grooves, true size	STEP · STL
picatinny-rail-9-slot	9-slot rail section, 90.07 mm long (9 x .394 in), MIL-STD-1913 profile and grooves, true size	STEP · STL
picatinny-rail-13-slot	13-slot rail section, 130.10 mm long (13 x .394 in), MIL-STD-1913 profile and grooves, true size	STEP · STL
picatinny-mount-jaw	Female profile for designing a mount: block with the MIL-STD-1913 rail removed and a .206 in recoil key; nominal, add clearance	STEP · STL

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Plain text: sheet.txt · JSON: /api/geometry?object=picatinny-rail-mil-std-1913