I have a question about "7mm Brass nut"

According to Martin "Sticky" Round's Workshop Manual ch. 10.4page 189, "the manifold is best retained by new spring or wavy washers and brass 11 mm head nuts." These are 7 mm and not 11 mm? Could you please clarify this ?

Question

I have a question about "7mm Brass nut"

According to Martin "Sticky" Round's Workshop Manual ch. 10.4page 189, "the manifold is best retained by new spring or wavy washers and brass 11 mm head nuts." These are 7 mm and not 11 mm?  Could you please clarify this ?

Accepted Answer

There is some confusion here, 7mm refers to the thread size and 11mm refers to the spanner size across flats.

A standard 7mm nut uses 11mm spanner size.

Nut plain brass 7mm, Lambretta exhaust port nut, extended, MB