I have an electric motor that has threads on the end of it. I'm interested in making a wood pulley to put on the end of it for use in a lathe. The only thing is that I'm not sure if I have the right tap or not. I measured, across the threads using a caliper, and got 9mm and using a TPI reader I got 1mm thread pitch. Does this mean that I need a M9 x 1mm tap to etch threads in the pulley so I can put it on the motor shank?
A little bit of research shows me that M9 taps are available in 0.5, 0.75, 1.0 and 1.5 mm pitch. This was a surprise to me. Your assessment regarding your measurements are correct, if your measurements are accurate enough.
To ensure one more level of success, consider to purchase a single nut of M9-1 and see that it easily threads onto the motor shaft. If it does, you can be confident that an M9-1 tap will do the job properly.
It is not unusual for a motor shaft to have a left hand thread. Purchasing a nut will also determine that aspect.
Consider that wood will require much more care when tapping such a fine thread. You will want very hard wood and also a sharp tap. Be sure to purchase the proper diameter drill to create a pilot hole in the pulley.
Additionally, you may want to use a nut insert, often known as a T-nut in place of tapping the hole. T-nuts are also available without the barbs, designed to be screwed to the surface.
If you are inclined to stick to wood alone, you can drill a hole slightly smaller than the appropriate size for the tap, then apply an epoxy that will soak into the wood, providing greater strength for the tapping process. Epoxy which takes longer to set will be stronger, that is to say, a five minute epoxy will cure quickly and be weaker than a one hour version.