Common T Slot Sizes
Choosing the right size screw and screwdriver bit configuration. Choosing the wrong screwdriver bit for your screw head can mean the difference between success and distress. By selecting the right match and fit you will prevent stripped screws, damaged bits, and spoiled work surfaces. Choose the bit size that fills the screw head entirely.
This information applies to the American Steel Industry.
- 20-2020 is a 20mm x 20mm metric 20 series square T-slot profile with four open T-slots, one on each 20mm face. The profile is smooth, which makes it resistant to dirt and debris buildup while also being easy to clean.
- These different sizes are measured in T-sizes. If you haven’t noticed it yet, you will see in the market these T-sizes whenever you are shopping for the perfect torx screws. It can see them in the exterior of the parts, but sometimes, they may be hard to find. Depending on the manufacturer, you can quickly identify the size of the screw.
- A list of the standard key sizes and corresponding keyways for Metric shafts are listed below in Table 2. The common specification dimension, Key Size, is highlighted. Metric Standard Parallel Keyway and Key Sizes Shaft Diameter (mm) Keyway (mm) Key (mm). From To Width (W) Depth (h) Width (W) Depth (T) 6 8 2 1.0 2 2.
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.
(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.
Common T Slot Sizes Diagram
You’ve probably noticed that in all homes built since the early 80s, the standard configuration for a receptacle is a large slot on the left, a smaller slot on the right, and a roughly circular hole in the middle underneath the two of them.
You probably know that the center hole at the bottom is the ground wire, but probably don’t know why one slot is larger than the other, or how grounding works exactly.
How Electric Circuits Work
The larger, left slot in a receptacle is neutral and the smaller right slot is hot. In all electric circuits, electricity flows from a point of higher electrical potential to a point of lower potential. The hot wire in a house is the source of electrical potential. It’s the one that will shock you if you touch it, and that’s why we call it hot.
Common T Slot Sizes Chart
When you plug in an appliance or light bulb, the current flows out the hot side of the plug to the appliance or light, and then back out of the appliance on the neutral wire into the left side of the plug, completing the circuit.
Polarized Receptacles
Remember that in order for an electrical appliance to run, a complete circuit must exist through the appliance. This means a switch could be placed anywhere in the circuit and still prevent the appliance from running. For example, on a toaster, the switch could be placed either before or after the heating wires in the circuit and it would be equally effective. However, it would not be equally safe.
Let’s say that we have a toaster with a switch installed after the heating wires. A piece of bread gets stuck in the toaster and you (unwisely) start rooting around inside of it with a metal fork. Since those wires are electrified (they are connected to the hot wire), as soon as you provide an alternate path for the electrical current to exit–e.g., through the fork, through your body, out your feet to the ground–you get shocked.
Take the same toaster and put the switch before those heating wires. Now, when you go rooting with a form, the wires aren’t electrified at all, and you won’t get shocked.
If it isn’t obvious already, the reason one side of a plug is larger than the other (a.k.a. polarized) is to make sure that the switch inside a device is always in the circuit before the motor or heating wires or other electrical parts. This is a safety mechanism just in case you accidentally provide an alternate exit path for the current.
Stay Tuned
Now you know about polarization. Stay tuned for how grounding works and why we need it.
(photo: oxymoron)