Where can I get greenhouse fixings for wire?

[madmaggot]

Any ideas where I can find some fixings, either aluminium or plastic, that slot into the greenhouse bars so I can fasten the support wire for my grapevine?
I want to train the vine onto the roof only so that it will provide shade in the summer.
I've searched on-line and asked at shops but no-one seems to supply them; if I knew what they might be called it would help though! ;-?

[madmaggot]

Many thanks Trim; now I know the sort of thing to ask for!
I'm going to town today so will see if I can get any there, otherwise I will be ordering from ebay.
Cheers.