Abstract: A breaker for roller chains includes a rigid frame with a chain receiving opening. A clamp member with an open pin receiving bore is mounted to the rigid frame on one side of the opening for adjustment along an axis. A punch block with a central bore is releasably mounted to the rigid frame on an opposite side of the opening. The punch block is located by a positioner with its central bore substantially coaxial with the axis. The punch block and clamp member include chain link engaging surfaces positioned relative to the opening to releasably clamp a roller chain with a pin thereof aligned with the axis and with the link engaging surfaces in clamping engagement with chain side plates adjacent the pin. A punch pin is slidably mounted within the punch block central bore, with a pin driving end movable through the opening and receivable axially within the pin receiving bore of the clamp member.