Pilot, not a solid column
The screw needs a bore. A solid boss sinks and cracks.
Self-tapping screw bosses
Self-Tapping Screw Bosses: Pilot, Wall Support, and Crack Risk
The screw cuts plastic. Size the pilot, core the boss, and tie it to the wall. DFM review comments on CAD, resin, and screw type before quoting.
Design guideline
The screw cuts the thread. The boss must survive it.
A self-tapping screw boss lets the fastener cut threads in plastic. Pilot geometry and wall support matter more than a thick solid cylinder.
Pilot diameter and depth control how much plastic the screw displaces. A boss isolated on a thin wall can sink or crack before the screw strips. Boss design owns the shared post. DFM review needs screw type and resin.
This spoke owns self-tapping pilots. Post-mold inserts and molded-in inserts own metal. Molded-in threads own plastic threads formed in steel. The design guide hub lists every topic.
Roles
Which page answers which fastening question
Stay here for screws that cut plastic. Open a sibling for inserts or the post.
| Page | Use it for |
|---|---|
| Self-tapping screw bosses (this page) | Pilot, support, and crack risk |
| Boss design | Shared post: core, draft, sink |
| Post-mold inserts | Metal installed after the shot |
| Molded-in inserts | Metal in the cavity |
| Molded-in threads | Threads formed in the mold |
| Gussets | Braces that keep a tall boss from cracking |
| Wall thickness | Nominal wall the boss should reference |
| Draft angle | Draft on OD and bore |
| DFM review | CAD check before quoting |
Checks
What DFM review looks for on self-tapping bosses
Qualitative checks. No figure on this page is a NetProto specification.
Wall or gusset tie-in
An isolated post on a thin skin fails before the thread strips.
Draft on OD and bore
Both faces need draft. The boss page owns the shared rule.
Resin and glass fill
Glass-filled grades are harder on bosses. Put the grade on the RFQ.
Decision
A thick cylinder versus a supported self-tap boss
Wrong: a solid pillar and hope. Right: pilot, core, draft, and a tie back to the wall.
What goes wrong
- A solid boss with no pilot
- A free-standing post on a thin cosmetic wall
- No screw type or resin on the RFQ
What to try first
- Call out pilot and screw type
- Core the boss and tie it to the wall or a gusset
- Use an insert if the joint must survive many cycles
RFQ
Send these notes with CAD for a self-tap boss review
The quote can start from CAD alone. These notes make the DFM pass specific.
Screw type and size
Pilot diameter and depth, if you have a target
How the boss ties to the wall or a gusset
Resin family, especially if glass-filled
Cosmetic face opposite the boss
Expected assembly cycles
Related
Related design guidelines
Stay on this spoke for its question. Open a sibling for the neighbor topic or the CAD check.
DFM review
How NetProto checks pilots and support.
DFM reviewFAQ
Self-tapping screw bosses FAQ
Can bosses be molded without inserts?
Yes. A self-tapping screw cuts threads in plastic. This page owns that path. Inserts are for joints that need metal.
Do self-tap bosses need draft?
Yes on the OD and the bore. The boss and draft pages own those faces.
What if the boss cracks in assembly?
Usually the post is isolated, the pilot is wrong, or the resin is brittle or glass-filled without support. Tie it back and check the screw type.
How thick should the boss wall be?
Size it from the nominal wall. NetProto does not publish a boss-to-wall ratio. The bosses page owns the shared post.
When should I switch to an insert?
When the joint sees many cycles, high load, or a resin that does not hold a cut thread. Open the insert spokes.
How is this page different from bosses or inserts?
Bosses own the post. This spoke owns the self-tapping pilot. Insert pages own metal. DFM review checks CAD.
Next step
Upload CAD for DFM review of self-tapping bosses
Share screw type, resin, and how bosses tie to the wall so review can check pilot, support, and sink before quoting.