The marks on the flats date to 54' - 89' so are from proving after the sleeving in 88'.
The 13 R (bore .710 - .718) and L 13/1 (.719 - .728) are from the original proving. It is possible that the other marks were filed off from the flats, or were lost when the tubes were cut; so we can't date the original proof.
The sleeved bore is .728"
3 tons is for a max. service pressure of about 9000 psi
Great Britain adopted the 1969 CIP standards March 1, 1980 but continued using Lead Crushers to measure pressure until 1989.
