Hamilton Standard 3-Bladed Hydromatic Model 43D conforming to
Propeller Type Certificate No. 851. Its used on a number of aircraft (Grumman Tracker, an maybe on the T-28)
Most S-2 had square tips, this prop was authorized on that airframe (actually the C-2) according to the FAA TCDS when flown in civilian use. This data is attained from the manufacturer. There's a possbility that the blade tips might have to be modified before use on a C-1 airframe, but the TCDS doens't mention that. All this is based on the information on the blade face.