It is important when fitting the layshaft and checking the tolerances in the gearbox, that the layshaft is pulled all the way into the rear hub bearing, as far as it will go.
Offer the layshaft into the bearing, fit the sleeve locating the allen screw in the layshaft grooves, fit the special nut provided, hold the sleeve with a spanner and tighten the nut until the layshaft is drawn into position, when it locks up remove the sleeve turn it around and re-tighten up.
Ideal to fit the layshaft and keep it tight so the gearbox can be shimmed up correctly.
TIP use some grease on the threads.
For more information on this tool please see page 26 and 97 in The Complete Spanner's Manual To Lambretta Third Edition (Green Cover) by Martin "Sticky" Round