A vehicle arm assembly comprising: a carrier base for attaching to a vehicle ; support arm rotatably mounted relative to the carrier base ; a first detent ring including a plurality of first detent projections circumferentially offset by a plurality of first detent channels ; and a second detent ring including a plurality of second detent projections circumferentially offset by a plurality of second detent channels ; wherein the first detent ring is fixed relative to one of the carrier base or the support arm and the second detent ring is fixed relative to the other of the carrier base or the support arm ; wherein the first detent ring is in an intermeshing arrangement when the second detent ring in a first rotational position and in a non-intermeshing arrangement when in a second rotational position; wherein in the second rotational position a first stop surface fixed relative to the carrier base is in engagement with a stop fixed relative to the support arm ; wherein the plurality of first detent projections include: at least two first projections each extending a first arcuate distance around the first detent ring ; and a single first projection extending a second arcuate distance around the first detent ring with the second arcuate distance being greater than the first arcuate distance; and wherein the single one of the plurality of first detent projections and one of the at least two first projections together extend an arcuate distance of at least 60 degrees and less than 120 degrees around the first detent ring . a carrier base for attaching to a vehicle ; support arm rotatably mounted relative to the carrier base ; a first detent ring including a plurality of first detent projections circumferentially offset by a plurality of first detent channels ; and a second detent ring including a plurality of second detent projections circumferentially offset by a plurality of second detent channels ; wherein the first detent ring is fixed relative to one of the carrier base or the support arm and the second detent ring is fixed relative to the other of the carrier base or the support arm ; wherein the first detent ring is in an intermeshing arrangement when the second detent ring in a first rotational position and in a non-intermeshing arrangement when in a second rotational position; wherein in the second rotational position a first stop surface fixed relative to the carrier base is in engagement with a stop fixed relative to the support arm ; wherein the plurality of first detent projections include: at least two first projections each extending a first arcuate distance around the first detent ring ; and a single first projection extending a second arcuate distance around the first detent ring with the second arcuate distance being greater than the first arcuate distance; and at least two first projections each extending a first arcuate distance around the first detent ring ; and a single first projection extending a second arcuate distance around the first detent ring with the second arcuate distance being greater than the first arcuate distance; and wherein the single one of the plurality of first detent projections and one of the at least two first projections together extend an arcuate distance of at least 60 degrees and less than 120 degrees around the first detent ring . <EOS>