How to Match Runner Lock Pins with Collars and Bushings
The Three-Component Assembly
A complete runner lock pin assembly consists of up to three components:
- Runner lock pin — The functional component with the gripping tip. Available in multiple tip types (standard, hard lock, edge, cone) and shaft types (straight, tapered).
- Collar (spacer) — A precision ring that sits between the pin head and the plate surface. Controls how far the tip protrudes into the runner channel.
- Bushing (optional) — A hardened sleeve pressed into the plate bore that protects the softer plate steel from pin-induced wear. Extends mold life in high-cycle applications.
Collar Sizing
The collar is the most critical pairing component. Its height determines the pin tip protrusion depth — the distance the tip extends into the runner channel.
| Parameter | Formula | Typical Value |
|---|---|---|
| Collar height (H) | Plate thickness − Tip protrusion − Pin head thickness | Varies by application |
| Tip protrusion | 30–60% of runner channel depth | 1.0–2.5 mm |
| Collar OD | Must match pin head OD | Pin head size + 0/−0.05 mm |
| Collar ID | Must clear pin body | Pin body ø + 0.1–0.2 mm clearance |
Tip protrusion that is too deep blocks resin flow around the pin tip, creating a dead zone where material stagnates and degrades. Too shallow and the tip cannot grip the runner securely. The optimal protrusion is 30–60% of the runner channel depth — enough to embed the undercut geometry in the runner while leaving room for resin to flow around the pin.
Bushing Selection
Bushings protect the mold plate bore and are recommended in these situations:
- High cycle count — 500,000+ mold cycles cause measurable bore wear, especially with hard lock tip pins
- Soft plate material — P20 or equivalent pre-hardened steel (28–34 HRC) wears faster than hardened plates
- Frequent pin replacement — Each pin change slightly enlarges the bore; a bushing provides a replaceable wear surface
| Bushing Feature | Specification |
|---|---|
| OD tolerance | h6 (press fit into plate bore) |
| ID tolerance | H7 (slip fit with pin body) |
| Material | SKD61 (H13) at 50–54 HRC typical |
| Length | Equal to plate thickness at pin location |
According to ScienceDirect's press fit engineering reference, H7/h6 interference fits for hardened steel sleeves in pre-hardened plates require careful temperature control during installation — either cool the bushing or heat the plate to achieve assembly without galling.
Size Compatibility Quick Reference
| Pin Body ø | Pin Head ø | Collar ID | Collar OD | Bushing ID | Bushing OD |
|---|---|---|---|---|---|
| ø4 | ø8 | ø4.1 | ø8 | ø4 H7 | ø8 h6 |
| ø5 | ø10 | ø5.1 | ø10 | ø5 H7 | ø10 h6 |
| ø6 | ø10 | ø6.1 | ø10 | ø6 H7 | ø10 h6 |
| ø8 | ø13 | ø8.1 | ø13 | ø8 H7 | ø13 h6 |
| ø10 | ø16 | ø10.1 | ø16 | ø10 H7 | ø16 h6 |
These are typical dimensions from the JIS B 5111 mold component standards. Always verify against the specific manufacturer's catalog — pin head sizes and collar dimensions vary between suppliers.
Assembly and Installation Tips
- Verify plate thickness — Measure the actual plate thickness at each pin location. Nominal plate thickness may differ by 0.05–0.10 mm from actual due to grinding tolerances.
- Trial fit — Insert the pin with collar (no resin) and verify tip protrusion depth using a depth micrometer before first molding trial.
- Collar stacking — If the exact collar height is not available as a single piece, stack two collars. Ensure the combined height matches the required dimension within ±0.02 mm.
- Bushing installation — Press bushings in at room temperature using a precision arbor press. Do not hammer — impact can crack the hardened bushing.
Frequently Asked Questions
What is the purpose of a collar on a runner lock pin?+
Do all runner lock pins require bushings?+
How do I determine the correct collar height?+
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