Standard T Slot Dimensions

The T-slots are designed to a specific depth and width depending on the material. The T-slot is used mostly for mounting and fastening a wide variety of accessories and panels to the aluminum extrusion. Often, panels will be inserted into the T-slot to quickly create a wall or enclosure. Made from C45 grade steel the 2020 t-slot plate has a smooth underside and can be easily suctioned on to a vacuum table. Making it easy to mount with vices, clamping towers, mounting angles and anything else you wish to clamp. Dimensions: 200 mm (7.87') x 200 mm (7.87') Profile height: 20 mm (0.78') T-slot spacing: 50. Bolt Size (d) T-Slot Size (a) L: Part. E: k: b: a1: Bolt Size (d) T-Slot Size (a) L: Part. E: k: b: a1: M06: 6: 25: 787-0606-025: 10: 4: 15: 5,7: M18: 20. When using Hole Callout to dimension a slot in SOLIDWORKS 2009 or later, this is the type of dimension that is inserted. Method (b) The third method (c) provides the width and overall length of the slot in linear dimensions. This method is preferred if the slot has positional tolerances that use the boundary method (see ASME Y14.5M-1994 figure.

M-LOK, standing for Modular Lock, is a free licensed^[1]firearmrail interface system developed and patented by Magpul Industries.

M-LOK allows for direct accessory attachment onto the 'negative space' (hollow slot) mounting points, and is a competing standard to VLTOR's open sourcedKeyMod system for replacing the ubiquitous Picatinny rail in some applications.^[2] Compared to the Picatinny rail system, both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and more fenestratedhandguard/fore-end with accessories mounted only where needed, whereas a Picatinny handguards typically will have rail slots for its whole length resulting in a heavier and bulkier handguard with sharp edges and poorer barrel ventilation.

The M-LOK system can be seen as an evolution of the Magpul Original Equipment (MOE) system, but the two are not fully compatible. Though newer M-LOK accessories can be used on older MOE slot handguards if an adaptor plate is used, there is no adaptor available for using older MOE accessories on the newer M-LOK handguards.

History[edit]

A prototype of the MOE slot was revealed by Magpul in late 2007 together with their Masada Concept Rifle (which would later be known as the Adaptive Combat Rifle). The MOE slot system was released by Magpul in 2009 as a feature on their MOE handguards, and at the same time compatible accessories such as Picatinny rail sections, direct MOE mounted light mounts, grips, bipod studs, etc. were released.

The MOE slot standard was never officially released, and a drawback to the system was that the rear side of the panel had to be accessed in order to mount accessories, limiting its application. The MOE slot system uses a weld nut which has to be placed manually on the inside of the handguard before mounting, making the slot system unsuited for applications such as free-floating handguards. Also, depending on the accessory item, the spacing increments between the MOE slots were not small or uniform enough to adjust the desired placement of accessories.

Acknowledging shortcomings of the MOE systems, Magpul drafted M-LOK as a new and improved mounting standard which was released in 2014 replacing the existing MOE slot. The M-LOK rail specification included metric dimensions instead of imperial, and utilizes a T-slot nut capable of only 90-degree rotation, reinforced by thread-locking fluid, making it suited for applications on free-floating handguards. It was designed to work with both metal and polymer parts.

In 2016, Colt Canada developed and released the Modular Rail Rifle (MRR) that uses a monolithic upper receiver with the M-LOK attachment system.^[3] In 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips, vertical foregrips, bipods, sling adaptors, and flashlight mounts.^[4]

In 2017, a summary report of testing conducted by NSWC-Crane for USSOCOM indicated that, while comparable in endurance and rough handling testing, M-Lok greatly outperformed Keymod in repeatability, drop testing and failure load testing.^[5]

Licensing[edit]

While M-LOK is free licensed, it is not open source, and thus manufacturers must acquire a license from Magpul before making products using the M-LOK standard. Magpul claims this gives them more control in assuring that all M-LOK products are made to specifications ensuring compatibility. Program participation is open to any interested manufacturer.

Technical specifications[edit]

Rail specifications[edit]

The slot dimensions (used on handguards, etc.) are available on the web.^[6] The slots provide metric 20 mm (0.79 in) length intervals, and accessories can be mounted either within a slot or bridging between slots, making it possible to adjust the position of accessories in smaller intervals than the length of the slot. The slots on an M-Lok handguard are approximately 32 mm (1.260 in) long and 7 mm (0.276 in) wide and space 8 mm (0.315 in) from each other. The radius of the corners is approximately 2.38 mm (0.094 in).^[7][8][9]

Attachment specifications[edit]

The quarter-turn T-slot nuts have different torque specifications depending on the handguard material:

• 4.0 N⋅m (35 lb⋅in) for attaching metal accessories to metal handguards.
• 1.7 N⋅m (15 lb⋅in) for attaching polymer or metal accessories to polymer handguards.
• 1.7 N⋅m (15 lb⋅in) for attaching polymer accessories to metal handguards.

Attachment screws made by many U.S. manufacturers are often either #8-32 TPI or 10-24 TPI UNC threads, which respectively have major thread diameters of 0.1640 inches and 0.1900 inches (4.166-0.794 mm and 4.826-1.058 mm expressed in metric designation). Many M-LOK screws on the international market instead use either M4 or M5 metric threads to reduce cost.

The tool required for mounting, in addition to the thread size, also depends the screw head type. Hex keys are used extensively in the firearms industry, but metric and imperial hex keys as a general rule are not compatible. It is possible damage the tool and screw by selecting a tool that is too small for the fastener, which can be done by using an Imperial/customary tool on a metric fastener, or the converse. An exception to this is 4 mm hex keys, which are almost the exact same size as ⁵⁄₃₂ in (3.97 mm). In many industries, this makes 4.0 mm (⁵⁄₃₂ in) hex keys preferred for consumer products because end users can successfully use an imperial key on a metric fastener, and vice versa.

While screw and slot dimensions are available on the web, the T-slot nut dimensions are currently under review by the US State Department to determine whether it should be regulated by ITAR, and until it is clarified drawings are only available to US citizens.

• M-LOK handguard and attachment parts

• M-LOK approximate slot dimensions. (Primary measurements in millimeters, inches in parenthesis).

See also[edit]

• Rail Integration System, generic term for a system for attaching accessories to small firearms
• Weaver rail mount, early system used for scope mounts, still has some popularity in the civilian market
• Picatinny rail (MIL-STD-1913), improved and standardized version of the Weaver mount. Used for both for scope mounts, and for accessories (such as extra sling mounts, vertical grips, bipods etc.) Major popularity in the civilian market.
• NATO Accessory Rail- further development from the MIL-STD-1913
• UIT rail, an older standard used for mounting slings particularly on competition firearms
• KeyMod - competing standard open standard design to M-LOK for mounting accessories
• Zeiss rail, a ringless scope mounting standard

References[edit]

1. ^'Magpul Industries - M-LOK'. Archived from the original on 4 December 2017. Retrieved 6 June 2016.
2. ^KeyMod vs. M-Lok: The Next AR Rail Standard by Chris Baker, November, 19, 2014
3. ^Colt Canada Modular Rail Rifle (MRR)
4. ^M-LOK Outselling KeyMod about 3 to 1, 28 January 2016
5. ^Details On The USSOCOM Sponsored KeyMod vs M-LOK Test Conducted at NSWC-Crane, 5 May 2017
6. ^Magpul Industries - M-LOK DESCRIPTION AND FAQ DOCUMENT^{[permanent dead link]}
7. ^'magpul.com - M-LOK 2015 FAQs'(PDF). Archived from the original(PDF) on 7 April 2019. Retrieved 7 April 2019.
8. ^M-Lok dimensions
9. ^Magpul M-LOK estimated dimensions

This information applies to the American Steel Industry.

Holes and Slots

Standard Holes

Standard hole sizes for bolts are made 1/16-in. larger in diameter than the nominal size of the fastener body. This provides a certain amount of play in the holes, which compensates for small misalignment’s in hole location or assembly, and aids in the shop and field entry of fasteners. In the absence of approval by the engineer for use of other hole types, standard holes shall be used in high strength bolted connections.

Although most holes for high-strength bolts are made 1/16-in. larger in diameter than the bolt body, certain conditions encountered in field erection require greater adjustment than this clearance can provide and approval from the engineer is required.

The maximum sizes of holes for bolts are given in the table below, except that larger holes, required for tolerance on location of anchor bolts in concrete foundations, are permitted in column base details.

Standard holes shall be provided in member-to-member connections, unless oversized, short-slotted or long-slotted holes in bolted connections are approved by the designer. Finger shims up to 1/4-in. may be introduced into slip-critical connections designed on the basis of standard holes without reducing the allowable shear stress of the fastener.

Oversize and Slotted Holes

When approved by the engineer, oversize, short slotted holes or long slotted holes may be used subject to the following joint detail requirements:

(1) Oversize holes may be used in any or all plies of connections in which the allowable slip resistance of the connection is greater than the applied load. Oversized holes shall not be used in bearing-type connections. Hardened washers shall be installed over oversized holes in an outer ply.

(2) Short slotted holes may be used in any or all plies of connections designed on the basis of allowable stress on the fasteners provided the load is applied approximately normal (between 80 and 100 degrees) to the axis of the slot. Short slotted holes may be used without regard for the direction of applied load in any or all plies of connections in which the allowable slip resistance is greater than the applied force. Washers shall be installed over short-slotted holes in an outer ply; when high strength bolts are used, such washers shall be hardened.

(3) Long slotted holes may be used in one of the connected parts at any individual faying surface in connections designed on the basis of allowable stress on the fasteners provided the load is applied approximately normal (between 80 and 100 degrees) to the axis of the slot. Long slotted holes may be used in one of the connected parts at any individual faying surface without regard for the direction of applied load on connections in which the allowable slip resistance is greater than the applied force. Where long-slotted holes are used in an outer ply, plate washers or a continuous bar with standard holes, having a size sufficient to completely cover the slot after installation, shall be provided. In high-strength bolted connections, such plate washers or continuous bars shall not be less than 5/16-in. thick and shall be of structural grade material, but not be hardened. If hardened washers are required for use of high-strength bolts, the hardened washers shall be placed over the outer surface of the plate washer or bar.

T Slot Nut Dimensions

(4) Fully inserted finger shims between the faying surfaces of load transmitting elements of connections are not to be considered a long slot element of a connection.

Nominal Hole Dimensions

Metric T Slot Dimensions

Anchor Bolt Holes

Standard T Slot Dimensions Metric

Hole sizes for steel-to-steel structural connections are not the same as hole sizes for steel-to-concrete anchorage applications. In the case of steel-to-steel connections, the parts are made in a shop under good quality control, so standard holes (bolt diameter plus 1/16″), oversized holes (bolt diameter plus 3/16″), and short and long-slotted holes can be used quite successfully. However, the field placement of anchorage devices has long been subject to more permissive tolerances (and often, inaccuracies that exceed those tolerances anyway and may require consideration by the structural Engineer of Record).

AISC published Steel Design Guide Series 1, Column Base Plates back in the early 1990s. At that time, it was recognized that the quality of foundation work was getting worse and worse. To allow the erector (and designer) greater latitude when possible, the permissible hole sizes in base plates were increased. These same larger hole sizes were included in the 2nd ed. LRFD Manual. The values there are maximums, not a required size. Smaller holes can be used if desired. Plate washers are generally required with these holes because ASTM F436 washers can collapse into the larger-sized holes, even under erection loads.

The larger hole sizes are primarily intended for the majority of base plates that transfer only axial compression from the column into the foundation. The anchor rods don’t usually do much after erection in that case.

To allow for misplaced bolts, holes in base plates are oversized. The AISC Manual of Steel Construction recommends the following oversized hole diameters for each bolt diameter:

Anchor Bolt Hole Dimensions

AISC, Steel Design Guide Series 1, Column Base Plates, suggests that using oversize holes meeting these criteria may still not accommodate field variations in anchor bolt placement and suggests adding 1/4 in. to the hole diameter listed. The guide recommends using a heavy plate washer over the holes. The AISC Structural Steel Educational Council cites the following example: “If bolts are misplaced up to 1/2 inch, the oversized base plate holes normally allow the base plate and column to be placed near or on the column line. If the bolts are misplaced by more than 1/2 inch, then corrective work is required.”

Based on AISC oversize holes, the AISC Structural Steel Educational Council recommendations, and concrete contractor anchor-bolt placement techniques, ASCC (American Society of Concrete Contractors) concrete contractors recommend the following tolerance for each bolt location:

• 3/4-in. and 7/8-in. diameter bolts: ±1/4 in.
• 1-in., 1-1/4-in., and 1-1/2-in. diameter bolts: ±3/8 in.
• 1-3/4-in., 2-in., and 2-1/2-in. diameter bolts: ±1/2 in.

Standard T-slot Dimensions

End of article.