ilikebikes, you need to use a 45mm fender or even a bit wider for a 27x 1 1/4 tire. The 27 inch tire is generally about 32mm wide. You should have a fender about 10mm wider than the largest tire you intend to run. That way you get enough coverage and enough clearance incase something ends up between the tire and the rim ( like an old syringe around K&A).

Also know that those fenders require drilling to fit your bike and unless your bike has a threaded rear brake bridge, you will need the bracket to attach the rear fender. Same with the front if you don't want to use the Dharuma(?) bolt. Just make sure all that stuff is included when you buy those fenders!