Brompton derailleur wheels The jockey wheels on the chain tensioner are made of a durable nylon material Over time these will wear and could help cause the chain to slip when under load It is common to replace the complete chain tensioner assembly - but it's possible to replace just the jockey wheels and associated components to save some money This derailleur jockey wheel pack consists of the following items: Pair of jockey wheels (idlers) for derailleur (2 or 6 speed) Brompton chain tensioners - 10 tooth Bearings (pair - approx 19mm long with a diameter of 6mm Fixing nut (approx 30mm long) and bolt (pair) Washer (pair) Dust cap (pair) It allows you to replace just the worn jockey wheels on a Brompton chain tensioner Tip: to keep your jockey wheels lasting longer (this applies to all drive chain components) - keep them clean from dirt / too much oil as this will cause them to wear quicker Tools required: 2.5mm allen key / hex wrench 10mm spanner small flat head / blade screwdriver