The diameter of the receiving hole of the Pivoting Door Holder Receiver # 37210635 is 9/16" of an inch. It is not meant to work on older featherlite horse trailers for the down window as a keeper, is it a replacement part for the Pivoting Plunger and Socket Door Holder for RV or Enclosed Trailer - 3" Plunger # 37210645.
I have added links below to video reviews of both parts for you to check out as well. view full answer...