On Sat, 09 Aug 2003 17:23:05 +0000, AMollitor did issue forth:

I need a square-taper bottom bracket for a road frame. The diameter is 68,
and the BB shell measures about 69 mm long. I want to use a Shimano 105
7/8 speed crank.

I'm looking at a Shimano BB-UN73. Are these square (as opposed to
splined)?

What length would be appropriate?

Yup, the UN73 is square tapered. Have a look here to find out more about
the spindle length you'll need:

http://www.sheldonbrown.com/bbsize.html#105

From your measurements, it'll be a 68mm shell.

Huw