Ridgid 42082 Model 500A Quick Opening Mono Die Head. The Model 500A Right Hand Die Heads Quick-Opening and Manually flips throughout lever to retract dies when Thread length is cut. Individual Machine Die Heads do not include dies. The Model 500A Die Heads replace the No. 500 Mono Die Heads. This Die Head is for use With Ridgid Model 535-535A-1822 Machines and 300 and 300-A w/carriage.