At a given insertion depth (D) of a drawbar (22, 60) in a trailer hitch receiver tube (24, 68), a pin arm (26, 56, 74) attached to the drawbar extends forward beside the receiver tube and holds a captive pin (21, 51, 76) beside a pin receiving hole (30, 71) in the receiver tube. A spring (36) urges the captive pin into the pin receiving hole to retain the drawbar in the receiver tube. The pin arm may be attached to the drawbar via a crossbar (40, 70, 73). Receiver tubes of different sizes (24, 68) may be accommodated by a drawbar size adapter (62) that slips over the drawbar, enlarging it, and by a vertical adjustment mechanism (83) for the pin arm (74) that aligns the pin with the pin receiving hole in either a smaller (24) receiver tube or a larger (68) receiver tube.