For the 1/12 car - We have 0, -1.5, -3 and -4. These have 3/16" axle for typical 1/12, Pro10 and WGT Tires.
For the F1 car - We have -1.5 and -3 - These have 5mm axle for F1 tires.

Less trail will generally make the car more responsive off center - more direct/twitchy feel generally. Going further back like a -3 or -4 will smooth the car out off center but will generate more mid/exit steering. Our eXcelerate Prodigy line of cars have seemed to be quickest in most situations with -3 or -4 steering blocks in all classes with the exception of -1.5's in F1 for outdoor asphalt or some driving styles that like a little more response from the front end to find their corner entry. We also use them at times in WGT-R just due to the heavier/higher bodies and roll those cars. -1.5's vs -3 will keep the car more flat mid corner. Hopefully this helps.