Rockwell Hardness Testers by the original US Wilson Company (then Acco Industries). Not a manual but a detailed explanatory Booklet from the 1980s describing how to determine which type of tester to choose for different jobs and materials with copious notes on the different types and methods to be used.

Matrix (Coventry Gauge and Tool Company) 55 and TT-712 Tap Grinding Machine. Detailed Service Manual with Parts as Sectional Drawings