Metric Fasteners
ESIII has an assortment of metric fasteners useful for many projects, and free for any team to use.
Types of fasteners
M3
M3 indicates a screw is 3mm diameter, as measured by the outside of the threads. These are common in electronics and good for small prototypes.
M4
M4 indicates a screw is 4mm diameter, as measured by the outside of the threads. These are common for hardware such as medium size motors, and good for larger assemblies.
Cap-Head
Cap head screws have a cylindrical head. They are the go to fastener in most situations. They are easier to model in assemblies and have a stronger socket than button-head screws.
Button-Head
Button head screws have an arced head. They are primarily used in situations which require a small head size, such as constrained space or exterior of a rocket.
Counter-Sunk
Countersunk screws have a circular head with a chamfer into the screw. These are good for situations which the top of the head must be flush with the surface. A countersink bit can be used to create a slot for the head in the material.
Standard Nut
Standard are have a hexagonal exterior and threaded inside to hold a screw in place. They must be held in place when screwing, either with your fingers (in applications which doesn't require a tight screw), with a wrench, or with a nut driver.
Square Nut
Square nuts are similar to standard nuts, but with a square exterior. These are mostly used for inserting in 3D printed pieces, as they create a stronger attachment and easier to install compared to standard nuts.
Nylock Nut
Nylock nuts have a small rubber contact on the head of the nut. This prevents the nut from coming undone with vibrations. These nuts should be installed with the rubber portion facing away from the screw head.
Heat-Set Inserts
Heat set inserts are used to create stronger threads in plastic components. They are installed by heating the insert (with a soldering iron), and pressing it into a hole in the plastic.
Self-threading screws
Self threading screws are used to fasten materials which don't have any threads. They can simplify components by not requiring nuts or heat-set inserts. They have larger threads compared with standard screws, and as the fastener is drilled, cuts into the material to create a thread and hold the screw in place.
Dimensions
Screw Dimensions
| Measurement | M3 | M4 |
|---|---|---|
| Thread diameter | 3mm | 4mm |
| Cap-Head diameter | ||
| Cap-Head length | ||
| Button-Head diameter | ||
| Button-Head length |
Nut Dimensions
| Measurement | Standard M3 | Square M3 | Nylock M3 | Standard M4 | Square M4 | Nylock M4 |
|---|---|---|---|---|---|---|
| Edge to Edge | ||||||
| Thickness | ||||||
| Circumscribed Diameter |
Hole Dimensions
Note that with soft materials such as plastic, standard screws can also be self tapping. These can easily be stripped by over-tightening however.
| Measurement | M3 | Self-Tapping M3 | M4 | Self-Tapping M4 |
|---|---|---|---|---|
| Clearance Hole | 3mm (1/8 in) | 3mm (1/8 in) | 4mm (11/64 in) | 4mm (11/64 in) |
| Tapping Hole | 2.5mm (3/32 in) | 2.2mm (3/32 in) | 3.5mm (9/64 in) | 3.2 (1/8 in) |
| Heat-Set Inserts | 5mm (3/16 in) | - | 5.5mm (7/32 in) | - |
Common Fabrication Dimensions
Because 3D printers produce undersized holes, tolerances must be adjusted from the actual values. These numbers are optimized for Prusa printers.
| M3 | M4 | |
|---|---|---|
| Clearance Hole | 3.2mm | 4.2mm |
| Tapping Hole (standard screw) | 2.6mm | 3.6mm |
| Tapping Hole (self-threading screw) | ||
| Hex Nut Width | ||
| Square Nut Width | ||
| Heat-Set Inserts | 5mm | 5.5mm |
| Cap-Head Clearance |
Because laser cutters produce oversized holes, tolerances must be adjusted from the actual values. This can vary with material size, focus, material and laser type.
| M3 | M4 | |
|---|---|---|
| Clearance Hole | 2.8mm | 3.8mm |
| Tapping Hole (standard screw) | 2.4mm | 3.4mm |
| Tapping Hole (self-threading screw) | ||
| Hex Nut Width | ||
| Square Nut Width | ||
| Heat-Set Inserts | 4.8mm | 5.3mm |
Re-order Links
Note: If a part is out of stock or requiring shipping from a different location, the "corrosion resistance" equivalent can be substituted, however slightly more expensive.
| Part | McMaster SKU | Link |
|---|---|---|
| M2 Socket Head, 4mm | 91292A004 | https://www.mcmaster.com/catalog/91292A004 |
| M2 Socket Head, 6mm | 91292A831 | https://www.mcmaster.com/catalog/91292A831 |
| M2 Socket Head, 8mm | 91292A832 | https://www.mcmaster.com/catalog/91292A832 |
| M2 Socket head, 12mm | 91292A834 | https://www.mcmaster.com/catalog/91292A834 |
| M2 Nut | 91828A111 | https://www.mcmaster.com/catalog/91828A111 |
*Unavailable from McMaster, order from Servocity instead