Knockout (ejector) rods transfer the press or machine stroke to the ejector plate, which in turn drives the ejector pins. In many tools the standard knockout rod is not long enough — the machine stroke starts too far from the ejector plate, or the tool sits on a riser, or the mold simply needs more travel. That is when a knockout rod extension is the practical fix.
Hex vs. round styles
Stock knockout rod extensions come in two common styles. The round style (PCS designation KR, e.g. KR37-10) is a straight round rod threaded to match the existing knockout rod, used where the rod runs in a guide bushing or close-fitting bore and a round cross-section is required for clearance. The hex style (designation KRE, e.g. KRE37-15) has a hex form that gives a positive grip for installation and lets the toolmaker hold the rod with a wrench while tightening the coupler — a real advantage when the extension must be locked against rotation or torqued reliably.
The number in the catalog designation encodes the rod size and length. As with all threaded ejection components, the thread must match the existing knockout rod exactly, and the extension length must be sized so that the coupled assembly reaches from the machine to the ejector plate with the correct pre-travel.
Coupling and alignment matter
- Confirm the thread size and pitch of the existing knockout rod before ordering an extension.
- Use a coupler that holds both rod ends squarely — misalignment at the coupler shows up as binding and uneven pin wear.
- For vertical tools, verify the coupled length and that the rod is not bottoming in the ejector plate bore.
- On high-cycle tools, check the thread engagement periodically; a loose coupler causes hammering and fatigue.
Because extensions are available from stock in round and hex styles across common rod diameters, you can usually extend a stroke the same day instead of machining a custom rod.
Catalog item plug: Tooling Components stocks PCS knockout rod extensions in hex (KRE) and round (KR) styles, matched to common rod diameters and lengths for ejector stroke extension.