There can be no doubt that a Myford ML7 fitted with a Tri-leva speed-change unit is a highly-effective small lathe, and one in good condition is well worth seeking out. The Tri-leva was a cleverly-designed unit that could be mounted on the headstock of an ML7 (but not Super 7) to perform both as a clutch and also allow instant changes of spindle speed to be made; it could be supplied ready-fitted to a new machine, or purchased as an aftermarket accessory.
The device consisted of a lower housing in die-cast aluminium that fastened into place under the headstock spindle by the use of three modified headstock-mounting bolts, each of which was threaed at both ends. The lower housing formed both a mounting shelf for the upper part of the unit and a guide for three permanently-mounted drive belts that formed the heart of the conversion. An upper housing held a similar belt guide and three spring-loaded roller selectors that could be pressed individually against the belt beneath them. An interlock disengaged one selector when the handle of another was pressed down.
The Tri-leva performed best when driven by a two-speed motor and many professional users, especially those intending to use the lathe for production work in the guise of the C7 Capstan Model, chose this option. Unfortunately, the entire set up was relatively expensive - in 1962 a Tri-leva unit, two-speed motor and its associated electrical-control gear added 35% to the £70 : 15 :  0d cost of  an ML7.