This should help choose the fastener you want.
http://www.mcmaster.com/#hex-locknuts/=jt06feI don't know if you know this next part already but if you do just skip it.
When using any self locking fastener don't forget to adjust the final torque values to correct for the added friction of the self locking feature.
Measure how much torque it takes to turn the self locking fastener and add that figure to the torque specified in the book for the fastener you are replacing, the sum of two is your corrected torque value for that fastener.
In this way the part gets the correct clamping load.
A word of caution about "Nylock" ( generic term nowadays ) nuts.
The plastic component comes in different materials hardness and durability, depending on the specifications to suite different applications and operating enviroments. Some have more grip than others, some are reusable and some are not. It all depends on selecting the correct spec for your application.
I hope this helps.