25S503 up for sale is a new set of 2 valve springs covered under lister Petter part number 571-10830 and also 291-20651 , valve spring some of our stock is on older brown craft heat sealed bags and do not have the lister petter bag with them , these are older US military stock , nice set of 2 new springs for your engine  
This spring is a spring within a spring 2 springs combined , 
the inner spring measures 1.156 outer diameter x 0.943 inner diameter x 1.969 free length x 0.104 wire size 
The outer spring measures 1.423 outer diameter x 1.171 inner diameter x 1.921 free length x 0.128 wire size , 

also covered under military NSN 5360-00-018-0284 , see our store for more items like this we add new items weekly to our store . Thank you rwk