1. Common T Slot Sizes List
2. Common T Slot Sizes Diagram
3. Common T Slot Sizes Explained
4. Common T Slot Sizes Chart

This information applies to the American Steel Industry.

Holes and Slots

Standard Holes

The caliper picture is fuzzy, but it looks like it reads 5/8' for the top of the T-slot, which is the common size for that sort of mill. A set of 5/8' T-nuts with 1/2' studs and 1/2' flanged hex nuts should be very easy to find. You probably will not find 5/8' T-nuts with 3/8' threads.

Common T Slot Sizes List

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.

• We have for years located the slot by the geometric centerlines and described the slot size by note. For example: 'SLOT 9/16 X 1'. Some of us are wanting to locate the slot with the longitudinal centerline in one direction and by the ends of the slot in the opposite direction. I haven't found any conclusive ANSI discussion.
• Flatness –.004″ per inch of width Straightness –.0125″ per foot of length, not to exceed.120 over 20 feet of length Twist – Twist per foot of length does not exceed.25 degrees and total twist over 20 feet of length does not exceed 1.5 degrees.

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.

(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

Anchor Bolt Holes

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.

End of article.

Many of the woodworking jigs and fixtures I make have at least one length of t-track built into them.

A t-slot aluminum extrusion provides an easy way to make jigs usable for different size workpieces as well as adding an adjustable clamping point for jig accessories such as stop blocks and toggle clamps.

This 1/4' t-slot track has a groove down the middle to keep the drill bit from wandering off center when drilling mounting holes.

A t-slot extrusion can be used in other places besides jigs. Use a pair on a router table to make an adjustable fence. Or use one on the fence to hold a featherboard or two.

Use them whenever you need to clamp anything anywhere along a straight line.

The two most common t-slot sizes are 1/4' and 5/16'. These two sizes will cover most every woodworking application. In fact, I use 1/4' most of the time because it's cheaper and plenty strong for what I use it for.

These t nuts and t bolts make it easy to attach clamps and other accessories to the t-track.

It is best to use t-nuts and t-bolts when attaching accessories to the track. Regular nuts and bolts can wreck the slot if overtightened.

If you have to use a regular hex bolt, use a small washer to prevent the head of the bolt from digging into the soft aluminum.

I like to get my t-bolts extra long and cut them down to the length needed for each application. This way I only need to keep one length in each size on hand.

Mounting the t track

No matter what your application, you'll have to cut a dado with either a table saw or router to mount the track flush with it's neighboring surface.

A 3/4' x 3/8' deep dado is cut to keep this t track level with the top of the workpiece. I cut this dado with the table saw.

Common T Slot Sizes Diagram

The 1/4' track that I use requires a dado that is 3/8' deep and 3/4' wide. The 5/16' track needs a dado 7/16' deep by 7/8' wide. I think these are fairly standard sizes, but always measure first before cutting.

Some t-track comes with pre-drilled mounting holes, but the version I like to use requires you to drill your own holes. They do however, provide a small groove in the center to help keep the drill bit from wandering.

Drilling your own holes takes a little extra time, but allows me to place them where it's convenient or necessary. I found with the other stuff, I was drilling extra holes where I needed them anyway.

Where to buy

I live in a small city of 35,000 people with only two major building supply centers. Trying to find stuff like this is maddening, so for years I've been ordering hard to find items online.

I get a lot of my jig parts from Lee Valley here in Canada. Look under hardware -- Jig & Fixture Parts. They have a very nice selection of top quality goodies, even if they are a bit pricey.

With the Canadian dollar hanging pretty close with the US dollar these days, I find myself hopping across the virtual border more often when I find great deals online. Online stores like Amazon carry a large assortment of t-track and related hardware.

One of the advantages of living in a large city is selection and availability of products. For those of us that prefer to live in smaller centers, the internet has evened the playing field. We can often get things shipped to our door cheaply and quickly for the same price a guy in the city might pay for gas running around to collect the things he needs. No white knuckle driving or one finger salutes... I love it.

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Common T Slot Sizes Explained

Common T Slot Sizes Chart