Heavy duty carriage buckle in traces, roller bolt style.  Came with a new carriage harness from "Golden Saddlery" These are wider than Smucker harness and measure about 1-3/8""  Great chance to replace some badly worn traces for safety.  These look good and should take a beating for marathon work.  I didn't have a carriage that accommodated this type of trace, so had standard traces made for the harness.  Hence they were never used.