Spare parts book. Suitable for 31C 2L 3L 9E 10E 11E 31A 32A 33A 34A 35A 36A 37A Motors. It has a technical data page with timing andset up stats. Also it has exploded diagrams off all assemblies along with part numbers. It also has charts with all gear ratios for road, trials, scrambles etc. Very useful book for seeing where parts go and working out what spec you have.