Brass Military Collar Pin, pre 1936

Brass Military Collar Pin, pre 1936, Nice Brass Military collor or uniform Pin. Has the screw back used prior to 1936. The Letter CT is on the button and after extenssive search, all we could determine is that the screw type was used until 1936. Any information is very appreciated. great collectible and since no other items can be found and military.com done have a reference, this must be a rare pin to add to any collection. Measures about 1.25 inch across.