The Spec Sheet Is the Contract
An ejector pin that binds, wobbles, or sticks is usually a tolerance problem — and the tolerance story is written on the spec sheet. The DMS Components catalog prints the same annotation block on every pin page: diameter tolerance, head tolerance, length tolerance, surface finish, and hardness profile. This guide explains what each number means and how to use it at the bench.
Diameter Tolerance: Where the Pin Meets the Mold
The body diameter is the critical fit dimension. On DMS nitrided pins the body diameter tolerance is -.0003 in. / -.0008 in. — a few ten-thousandths undersized, never oversized. That one-sided tolerance is deliberate: the pin must slide freely in the ejector hole without rocking, and an oversized pin would gall or stick. When a pin binds, measuring the body against this block tells you instantly whether the pin is out of spec or the hole is.
Head and Length Tolerances
The head diameter tolerance is +.000 in. / -.002 in. — held slightly under nominal so the head seats cleanly in the counterbore without a press fit. Head thickness (T) is also held to a minus tolerance of -.002 in. Overall length is a different class entirely: +.060 in. / -.000 in. on standard nitrided pins, meaning the pin can be up to 1/16 in. longer than nominal but never shorter. The reason is simple — a long pin can be ground to fit at final assembly; a short pin is scrap. Through-hardened pins use a +.375 in. length allowance because they are frequently trimmed to final length in the mold shop.
Surface Finish and Hardness
The working surface is held to 8–10 RMS — smooth enough to slide without galling and to release the part cleanly. The heat treatment block, as covered in our nitrided vs. through-hardened guide, is the other half of the story: 65–75 Rc surface with a 39–43 Rc core for EP pins, 65–74 Rc surface with a 50–55 Rc core for RHX pins, and an annealed head at 30–35 Rc so the head can take ejection impact without cracking. The tip is limited to a 1/32 in. radius maximum.
Verifying Incoming Pins
A 10-minute bench check settles most disputes: micrometer the body in two places, check the head diameter, compare overall length to the class tolerance, and confirm the pins are within the published numbers. Pins that pass the spec sheet but still bind are a hole or alignment problem — pins that fail it are a supplier problem. Either way, the answer is on the sheet.
Tooling Components stocks DMS ejector pins in the full tolerance classes and can help you verify a spec. Call (800) 992-4766 or visit www.toolingcomponent.com.