Here is the Hall sensor I use in my Oxyboxer and Type 4 crank trigger packages. It is dimensional the same as a Honeywell GT101, but has an internal pull-up resistor and offers wider gap tolerance.
Operating voltage: 4.75 to 24 volts
Maximum over voltage and reverse voltage: +27 to -25 volts
Maximum output current: 20 mA
Maximum frequency: 15 kHz
Temperature range: -40 to +125 degrees C
Maximum air gap: 5 mm
The trigger wheel must be at least 2 mm wide, the teeth and gaps at least 2 mm wide, and the gaps at least 2 mm deep.
Red - 12v Switched Power
White/Blk - Output Signal
Black - Sensor Ground