One pulse per rev is exactly what you need but afraid I think that will be too short a pulse if you are using the parallel port, if you have a SmoothStepper then it will be fine. You can lengthen the signal with some electronics but the easiest thing to do would be as Brett said and get an OPB 917B opto switch and a 220 Ohm resistor, in the UK that would cost about £6 (under $10). You could then fit a single slotted disc (around 10mm width slot) and threading will be no problem at all
I use that on both my mill and lathe and the lathe threads perfectly, see below, in the first pic two were done with parallel port and the other 2 were with SmoothStepper. Have also attached a pic of the sensor on my Bridgeport.
Hood