I have had both these tapping guides in my shop for about twenty years and they have paid for themselves time and time again.
Part number 2548A12 Tap & Reamer Aligner, for tight spaces or general use. My unit has a two notches on the bottom so that you can use it on a pipe, round tube or round bar.
Part #2704A12 Manual Tap Driver. I have never snapped a tap using this unit. Holes can also be tapped much faster with it than with a wide handle tap wrench.
http://www.mcmaster.com/#tap-wrenches/=4kumz6
I have seen these at low buck tool suppliers for less $$ I'm sure that the internet will have many sources.
Arthur