Long service awards engraving - help, quick please!

[LightShinesInTheDarkness]

I am having some long service awards engraved. They are expensive and important!

Which is correct, please?

25 years service

25 year's service

25 years' service

and your reasoning is .....?!!

It is really 25 years of service, isn't it? So it would not be possessive. The service does not belong to the year.

So I think it would be 25 years service. In the same way you would say 11 months old, or in 2 weeks time.

Actually, I'm not absolutely sure about what I've said, so please ignore.

Could you put '25 years of service' to avoid this?

Oh, shame you are not sure RB, as yours was actually my reasoning, almost word for word.

Anyone else?

I'd go with '25 years of service' to avoid any mistake!

It's just a plural, I think - there is no possessive in it so you don't need an apostrophe.

I think it is 25 years' service (service of 25 years). But would agree that 25 years of service sounds more formal and avoids whole issue.

This has been bugging me so I've looked online. As far as I can see we're all right because although the service does, in a sense, belong to the year, inanimate things do not usually possess other things and putting 'of' in is more correct.

So, you would not say, 'the book's matches were wet', you would say the book of matches was wet.

There are, apparently, exceptions to this rule such as 'razor's edge'.

Thanks for all your help!
We had spent ages researching as well, and had come up with different answers.
We went with 25 years service in the end.

It is generally accepted that it should take an apostrophe: 25 years' service. However, there is a strong argument that the possessive should not apply because it's not a true possessive. At this point, though, that battle has not been won. I'd have gone with the apostrophe.