The Tuning Works
spring Made in the UK for Aprilia Mk1. (they only have 1 spring)
This spring unlike most after market springs is linear rather then progressive and rates 15% stiffer than the stock spring.
You can send your Forks to TTW to be converted:
Made in the UK:
35 mm max o.d.
24 mm i.d. aprox
120 mm travel