Paul I think because you took the 2nd pic uncoupled it looked awkward but fitted they are not only easy to use but to a car person like a magnet they go for them and stick to them. Any thing car oriented is gold in the hand. Go to a garage etc do not say anything ask a question ask for a card of theirs pull out your assembled pen write anything and observe the reaction ( magic unfolds). Another winner is to be selective with tiny badges VW, FORD etc incorporate them or car stamps or vintage cars small transfers.
They have been around some time now but the novelty lingers strongly.
Love your pen and thoughts let us know the receivers reactions, sure to please no end. Thought for today keep a stock of the half sized biro refills.
Kind regards Peter.