I have brought home Auto parts from USA to UK before and the simple rules are, Wrap it best you can ensure there is no sharp or pointy edges that will stick in the machines and check it in, You wont be able to carry something like that in the cabin especially if it is deemed by security as a danger. rolled up carrier bags should be good to protect the ends. also bear in mind it will be treated as a "bag" so may be in addition to your allowance although that is all dependant on the agent checking you in