Ok here is the little nylon go-nogo gauge Triumph send with their spacer, you'll find both are grossly over priced. So instead of wasting money on them i make the spacer which can be easily made out of a 10mm or 3/8 inch bolt shank. You cut a piece of the shank to .355 inches long or 9mm. Now with the center nut, copper sealing washer, and spring out of the tensioner you just stick the nylon plug in as per the manual if the shoulder bottom to the tensioner you add the spring. If not you put the center nut and copper washer back on and torque. If it does then you add the spacer stick the spring back in and then sealing washer and center nut to torque spec.
So why make the spacer unless you have a lathe. the distance the gauge is measuring is 16 mm so I measure with a caliper. like below.
first the face of the tensioner and the shoulder of the plunger you will be measuring down to shown by the two yeller lines
next measuring the drop and yes this is done with the tensioner in the engine I am just using a extra one for the pictures.
if the drop is 16 mm or more it requires the spacer. and if memory serves me right The total travel is 23 mm
hope this helps