Here we have a CTC Yamaha TY 250 / 350 mono 84-92 Heavy Duty fork spring upgrade kit. 
This kit comprises of the following parts:
1 x Pair of CTC HD +10% Linear Fork Springs (replaces Yamaha Part Number 38V-23141-00)  
1 x Pair of CTC HD +10% Damper rod rebound springs
1 x Pair of CTC Adjustable fork spring pre-loaders
1 x Pair of CTC Damper rod seals
These are British made linear springs that are 10% stronger than the original Yamaha springs that are no longer available.