| Internal thread standard, nominal size and pitch |
Critical because the insert must match the mating screw exactly. |
Confirm whether the assembly uses a metric or inch thread, then verify the nominal size, pitch and required engagement length. A matching nominal diameter with a different pitch will not provide a usable threaded connection. |
A drawing may call for a fine-pitch internal thread even though another part of the assembly uses a coarse-pitch thread of similar diameter. |
| Insert style and installation method |
High because the design determines hole preparation, tooling and installation control. |
Compare self-tapping, wire thread, key-locking, press-in and heat-set designs according to the available hole, equipment and production process. Installation simplicity can involve a trade-off with preparation requirements or resistance to movement in the parent material. |
A press-in design may suit a prepared hole and controlled assembly process, while a self-tapping design may be considered where a separate internal tap is less practical. |
| Parent material and resistance to movement |
High because the same internal thread can behave differently in metal, plastic, wood or composite material. |
Evaluate the material's hardness, wall thickness and tendency to crack, deform or strip. The outside thread, knurl, flange, body length and installation method should support the required pull-out and torque resistance. |
A softer plastic component may need a different external profile or longer body than a thicker metal component using the same mating screw. |
| Body length, usable hole depth and wall thickness |
Important for seating, thread engagement and clearance inside the part. |
Select a length that provides the needed engagement without bottoming in a blind hole, breaking through an opposite wall or leaving insufficient material around the insert. Check the available depth rather than relying on the screw length alone. |
A blind-hole assembly may require a shorter insert than an open-through-hole assembly with the same internal thread. |
| Repair application or new production assembly |
Important because the design objective changes the preferred dimensions and insert construction. |
For repair, preserving the original screw size and restoring a damaged hole may be the priority. For new production, repeatable installation, serviceability and resistance to repeated screw removal may carry more weight. |
A replacement insert for a damaged threaded hole may be selected to retain the existing fastener, while a new plastic housing may be designed around an insert with a more suitable external holding feature. |
