A punch assembly for a punch press has a punch housing with a punch that is slideably mounted for reciprocation along punch axis within the punch housing and at least one resilient member in the housing for yieldably biasing the punch upwardly in the housing along the punch axis. A punch length adjustment subassembly is provided in the punch housing. The subassembly has a base member that is slideable axially but non-rotatably mounted within the housing and a punch head member having an upper end that is positioned to be struck by a punch ram of a punch press for driving the punch downwardly to an operating position. The punch head is mounted for rotation on the punch axis relative to the base member but is held against axial movement relative to the base member. The punch head is operatively associated by a threaded length adjustment connection to the punch and a releasable stop member is connected between the punch head and the base member for preventing rotation of the punch head relative to the base member while the punch assembly is in operation on the punch press. The invention is also directed to the punch head subassembly per se as a retrofit insert to update existing punch assemblies for manual tooless punch length adjustment and tooless punch removal.