New style Pilot RC Axles designed with a machined shoulder and nyloc nut so there is no need for collars.
Sold as a pair
A: Thread: 8mm dia x 15mm long
B: Shoulder (including hex) 7mm dia x 13mm long
C: Axle shaft: 4mm dia x 20mm long
D: Lock nut:M4 x 7mm
Weight: 16g per axle incl. nuts