The same gaskets used in all Pista pumps for 60 plus years, still produced by hand in Milan, Italy- Made from finest full grain leather, 2.5mm thick- 731 fits 28mm internal diameter Silca pumps (formerly 73.1)- 741 fits 30mm internal diameter Silca pumps (formerly 74.1)- 751 fits 19mm internal diameter Silca pumps, post-2015 Impero Frame and Pocket Impero pumps- Reusing the original nut can lead to later loosening of the assembly as the nylon insert will take a set over time. A new bolt kit guarantees years and years of trouble free service.