Engineering. Engineer using a thread-grinding machine, a machine designed to produce helical screw components. These can vary in size and use, from large rotors to worm gears. These need to be precisely engineered to ensure the correct pitch (angle of the spiral). This is the grinding head of a TG150E thread-grinder, with a spindle speed of 75-4000 revolutions per minute (rpm) and a maximum wheel width of 7 centimetres. The engineer is an employee of Holroyd, a manufacturing company that specialises in this technology. Holroyd, now part of the Renold Group, was founded in 1860.