Borgeson - Steering Coupler - P/N: 313449 - Welded Steel Steering Coupler. Fits 3/4 In.-36 Spline X 3/4 In. Double-D.Using a 2" straight extension, called a coupler, to extend the steering box, R&P shaft or the column shaft, can sometimes eliminate a universal joint. The coupler can be welded or pinned to the un splined end of a shaft. The 1" 48 and 1" DD couplers have a 1 1? 4" hole that will accept either an adapter to reduce inside diameter to 3 4" smooth or another splined or 3 4" DD coupler. The coupler assembly would have to be pinned and or welded together.