The two types of special nut shown below are made from David Fellows 5/32" Whitworth Full nuts.
I made my own from 4 B.A. full nuts and they can be converted to Meccano use simply by running the 5/32" x 32TPI Whitworth tap through them.
Note: 4 B.A. nuts are 1/4" A/F and therefore are the same size as Meccano nuts.
The types illustrated have been made by engineering fitters since long before I was trained when they had to improvise. David introduced the Meccano threaded versions at a meeting and I immediately saw the potential so I bought 500.
The two on the left (A) are all metal self locking nuts based loosely on the Aerotight design patented by GKN many years ago.
The two on the right (B) are described as captive nuts but are more commonly called in the sheet metal work trade as "Hank Bushes" or "Riveted Nuts", and in this case they are made from the same basic nut or they can be made from 4 B.A. Full nuts as described earlier.
Referring to A & B: the nut is held on a mandrel and the shoulder is the same length in both cases, half the thickness of the nut.
The shoulder diameter of A is 0.218" (7/32"), and nothing else is altered on the nut at this stage. The sawn slot across the face should be to the same length as the shoulder.
The shoulder diameter of B: the hank bush is Ø 0.185" and the first thread is removed by a countersink bit before turning the shoulder to facilitate riveting.
Holes in plates to be fitted with hank
bushes should be drilled with a Ø 3/16" drill, de-burred and lightly
countersunk on the correct face to accept the nut which will be permanently
riveted in position. Therefore any part so altered will be ’dedicated’
as a special part with possible limited use.
No 1 Mandrel: Turn a short length 1/8" x 5/32" dia on a piece of Ø 1/4" Brass x 1-1/4" long and thread it. This will be used to hold the nut while the shoulders are turned on both types.
Hank Bushes: Riveting is carried out with a 4 oz ball pein hammer using two suitable punches made from any piece of Ø 3/8" Mild Steel with a ball end as the first stage, and another with a flat end to finish the process.
Tool No 2: For Self locking nuts I suggest making a similar mandrel to No 1as a holder to be used in the Vice while the saw cut is run across the face.
Tool No 3: Is a piece of 3/8" Mild steel
with a 45 º hollow end. This is used to de-form the shoulder to provide
the self locking method.