Sprue Bushings: A, B and U Series
The sprue bushing is the entry point of the injection mold: it receives molten resin from the machine nozzle and directs it into the sprue and runner system. Because it seats directly against the nozzle, its head style, radius and length have to match both the machine and the mold plate.
Get those wrong and you get flashing at the parting line, poor seating, or a bushing that interferes with the mold base.
A, B and U series
Sprue bushings are commonly grouped into series that define the head style and the sprue geometry.
| Series | Head and geometry | Typical part number |
|---|---|---|
| A series | Standard straight head with a radius to match the machine nozzle | A129512 |
| B series | Extended-length variant, used when the sprue must reach deeper into the mold | B129512 |
| U series | Universal / full-round head style, for a longer, larger-diameter sprue on high-flow or high-cavity tools | U157512 |
Each series is stocked in a range of overall lengths, and the part number identifies the series, head style and length together.
Three measurements drive the selection
- Head style and diameter - must seat against the nozzle and clear the locating ring.
- Overall length - must reach from the top of the sprue plate to the runner plane.
- Sprue diameter - controls flow and pressure drop into the runner.
The head spherical radius should match the machine nozzle tip radius for a positive seal without excessive force.
Common replacement mistakes
- Ordering by the old part without measuring length - a bushing a few thousandths too short will not seat, and one too long bottoms out.
- Mixing head styles - an A-series head may not clear a locating ring recess designed for a U-series head.
- Ignoring the nozzle radius match, which causes flashing at the sprue bushing seat.
- Forgetting that the sprue bushing OD must clear the locating ring bore with running clearance.
Measure these four numbers before you order
- Head diameter and height
- Overall length
- Sprue entrance diameter
- Nozzle radius
With those four numbers we can match a stock bushing or identify the exact catalog number. Tooling Components stocks sprue bushings in A, B and U series from DMS, PCS, Superior Die Set and Progressive Components, sized by length and head style, plus the matching locating rings and nozzle adapters.
Send us those four measurements and we will identify the bushing. Request a quote or call 814-438-7657.