ultegra hub with a 105 cassette

I just had open pro wheels built with ultega hubs and went to install the casette but it doesnt seem to fit. Are there online instructions anywhere or are they not compatible?

It should fit. The cassette should have come with a spacer to put on the freehub first.

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"All that we see and seem is but a dream, within a dream..."

Sheldonbrown.com has a very nice article on shimano cassettes and freehubs. is it an old cassette and a new hub? how many speeds? if this is older equipment there may be compatibility issues

The bike is a 2004 specialized allez elite which i beleive comes with mostly 105 equipment.

Ultegra & 105 should be completely compatible. Did you line up the skinny spline on the freehub with the skinny slot in the cassette? (Sorry--don't mean to offend, but it seemed an obvious question to ask.)

I got it on, after taking off what i think is called the freebhub that came off the rear wheel and was still atached to the cassette.

Problem is, there is a gap that makes the cassette fit on loose. its about the width of a sprocket. Should i add another sprocket or will that not work with my current 105 shifters?

Gotta decent bike shop around? Go there, show them the wheel, it's what they do....

there are spacers to fill in the gaps