Hi all, just FYI:
I was having difficulty finding a coarse spline front sprocket / lock washer for a 520 chain in the UK without paying £80 plus P&P.
But I found a Spanish company Vitesse Engineering who provide this JT 15 tooth item, with 1mm spacers that can be used to position it correctly on the gear shaft.
The sprocket is only 16 Euros, the lock washer 6 Euros, and the spacers 3.60 Euros each.
Shipping to the UK was 18.15 Euros.
Overall sprocket thickness is 10mm
https://vitesse-engineering.es/en/categoria/engine/Cheers
Rob