They will never be loose because the one great thing that the designers did when desinging these parts was to taper them , so as the plastic wears it wil just push further and further in,
When I worked in product development one of my first big progects was a machine manufactured by this company for my company, they wouldn't even change the tooling to make it to our specs, it was all 36, thats the only size they made. I had endless arguments with them about it, Thats why I know for a fact that its 36 not 35, infact very few manufacturers use 35, AEG did. Its a odd number, Your vacuum hoses are made in 32, 36, 38 &50 mil those are the standard sizes used by most manufacturers. deviate from this and it becomes very very expensive. to give you an idea, the mould machine used to make a 32 mil hose cost £ 1 000 000 10 years ago