Wilwood 120-8924 CALIPER-GM METRIC 54 IRONWilwood 120 8924 CALIPER GM METRIC 54 IRON These are all new and not rebuilt, cast iron calipers, purpose built for racing. Wilwoods GM Metric Calipers are bolt on replacements for 1978 and later GM Metric calipers widely used in "spec" racing categories. Wilwoods new 2. 50 piston GM Metric calipers are now officially approved for IMCA as OEM replacement caliper that meet all rules in Modified, Stock Cars, Hobby Stocks, Northern and Sothern Sport