These are complete pistons with gudgeon pin, circlips and genuine Hepolite piston rings and are for the Triumph 500cc models. These particular pistons are + 20. They are made in England to very high standards and are as good as the original Hepolite pistons. These are superb quality at a very competitive price. The OE part number is 70-6907. They have a 7.5:1 ratio.