The True Radius sear differs from my standard Extreme Service sear in that the sear nose primary contact surface is ground (and then polished) in a radius true with the sear pin hole, hence True Radius. Standard sears have the primary contact surface ground in a flat plane.
In operation, the TR sear keeps even contact with the hammer hooks, so the hammer keeps neutral engagement with the sear. Life span is expected to increase, the part works well even in frames that have less than ideal hammer & sear pin spacing and parallelism and is much easier for the novice user to fit and get good trigger pull results.
1911, Issue:11, Page:019
Big Book Catalog, Issue:68, Page:119