typical method in the 19th century through 1930s. It is simple and useful, but the degree of control of concentricity is not quite good enough to be foolproof for high-speed, high-precision work (high precision can be achieved, but the time and skill involved in the setups makes it a poor choice now that better options exist, such as the cam-lock spindle noses described below). Threaded spindle noses are still built on new machine tools, but only of the low-end variety (hobbyist, least-expense MRO, etc.). High-capital manufacturing (where high upfront expense yields lowest possible unit expense for mid- to high-volume part counts of high-precision parts) has moved away from this type of mounting. The exact-adjust (Set-Tru) concept is one way to chase high concentricity on threaded spindle noses with some relative degree of ease. A common solution on smaller lathes is a broad flanged end to the spindle with a concentric raised circular register matching a recess in the chuck or its backplate. The register is normally shallow and parallel sided and a light push fit in the female register of the chuck. The chuck is held in place with bolts through clearance holes that do not affect the alignment which is entirely provided by the register. This arrangement has excellent repeatability but is slow in a production situation. A backplate with a female (self-releasing) taper may seat on the matching male taper of the tapered spindle nose (for lathe work) or of an adapter plate with the same nose, to be mounted on a table. This system improves the repeatability of the mounting concentricity down to a very small total indicated runout (TIR) value. Subtypes: The chuck may be held against the taper with a threaded retainer ring (large thin nut), typically wrenched with a spanner wrench of the pin or hook variety. The peak of popularity for building this type of spindle nose was the 1940s and 1950s. The chuck may be held against the taper with cam-lock posts that wedge into a stuck-fast position. Industry-standard spindle nose designs allow wide interchangeability. This cam lock spindle nose system replaced the earlier systems on most machine tools in the 1960s. Mounting of collet chucks For collet chucks mounted on backplates, all of the same methods above are applicable. Many lathes that run collet chucks have dedicated collet-closer setups whereby there is no backplate, and the spindle nose contains the female