A thread design first proposed in 1884 and then adopted in 1903.

The thread sizes are designated by a number from 0 to 22.

0BA is 6mm in diameter and has a 1.00mm thread pitch. 

The sizes then progress with each larger number screw having a pitch of 0.9 times the pitch of the previous size. (0.9p) The result is rounded to two significant figures in metric and then converted to imperial and rounded to thousandths of an inch.

The major diameter is 6 x the pitch.

The hex size is 1.75 x the major diameter

The pitch diameter of the thread is simply OD − 0.6p 

The minor diameter is OD − 1.2p.

The thread angle is based on the Swiss Thury thread, but is not quite the same. BA screws use a thread angle of 47.5° exactly and the thread form to be symmetrical with a depth of 3/5p.

The British Standards Institution  recommended the use of BA sizes in favor of the smaller Britsh Standard Whitworth (BSW) and British Standard Fine (BSF) thread sizes below 1/4".

BA threads found common use in electrical goods made in the UK and its colonies. It can also be found connecting the barrel of a dart to its shaft.

Very popular still with model engineers who find the head to screw diameter relationship desirable.

Further reading:

Are BA Screws Metric or Imperial? (stubmandrel.co.uk)

First Report of the BA Committee on small screws (sizes.com)

Second Report of the British Association for the Advancement of Science's Small Screws Committee, 1884. (sizes.com)

Ref: British Association screw threads - Wikipedia

Suzuki T20 Muffler-Exhaust Pipe Connector 14771-11040

I needed a couple of connectors for my bike and as I could not locate any to buy, I figured I had to make some for myself. I put my wealth of experience making this sort of thing, which was absolutely zero and off I went. My process is below.

Original part

Original part

New part test fitted to bike

Experience Requirements

• Basic lathe operating skill to turn up the mould
• Zero experience with silicon and making plastic/rubber/silicon parts is apparently ok.

The Mould

I used solid bar aluminium, 50mm diameter, turned up in a lathe for the inner part and aluminium pipe 60mm x 5mm (wall) for the outer mould. The outside diameter of the part was thus set by the inside diameter of this pipe (close enough to give it a try I thought).

Re-machining the inner mould

The outer mould would have been better made from pipe 60mm x 10mm to allow the exact outside dimension of the gasket to be made, however this was more expensive to buy so I thought I would attempt the cheaper option first and see how the process workout out.

I chose aluminium over steel as it would not rust in storage and it is cheaper than brass. Possibly the mould could be made from nylon or similar bar, however I do not have much expertise turning nylon as so went with the aluminium.

Measuring the internal/external diameters of a soft flexible part was somewhat problematic. My first attempt at an internal mould was discarded before use other than as a tool to help with sizing of my second attempt.

The mould pieces

Make stepped inner mould long enough to hold in vice for mould separation purposes. Mine was 100mm long.

Outer mould ring – make 5-10mm longer than total length of part. Mine was 38mm long

The outside diameter of my part is larger than the sample due to cost of aluminium stock.

The total length of my part turned out 1.5mm longer than the sample. I initially thought it may be easier to pour if the inner mould part was a little longer. This was unnecessary as it turned out. I could have easily been reduced the length; however, it caused no issue with fitting, and as such I was happy to leave as is.

The Material

After much research and really finding nothing to help I chose:

Firm Addition Cure RTV-2 Silicon M4670

Hardness Shore 55A

Approx. 25g of silicon is required to make the part.

Mix slightly more than this as some silicon material will remain in the mixing container.

I found 30g + 3g (Part A + Part B) was sufficient, with little waste when making a singular part.

The silicon is a beige colour but can be tinted orange if desired. This would have added to the cost and as the part is not really visible and I did not know if the part would even turn out I chose not to spend the extra.

I think it would be better to draw a vacuum on the silicon mix to remove air bubbles before use. I did not have anything to do this and as such I didn’t bother. A few bubbles came to the surface in the first ½ hour or so of setting. I popped these with a toothpick. The final resultant part did not show any signs of air bubbles and thus ruining the part so maybe drawing a vacuum is a bit over the top.

There was no evident shrinkage of this material upon setting.

Coat mould parts with a graphite powder to act as a mould release.

A couple of dobs of hot melt glue secures the outer ring to the inner. This glue is easily removed when no longer needed.

\

At first, I used kitchen scales to weigh out the silicon for mixing. This was OK, but I did find that these scales are not accurate enough for the small quantities I was mixing. Although the scale resolution was 1g the accuracy did not match. After a failed attempt that turned into a sticky blob I borrowed a better scale.

A few prods with a stick just during pouring to help release any trapped air pockets.

(Note: the slit in the outer mould does not go all the way through and was part of an early attempt in trying to work out how to release the part from the mould pieces.

Setting takes 24 hours.

Releasing the part from the mould can be problematic.

In the end I chose to hold the inner mould piece in the vice and use a chain pipe wrench on the outer part. The twisting action that results released the parts without damage.

The part above is discoloured due to the graphite powder used for mould release. This can be cleaned somewhat, but I did not bother.

Conclusions

I am happy with the end result. The larger diameter part caused no problems in fitting, but being a bit retentive I would prefer to reduce the outer diameter to match the original.

Ideally, I would like to make at least two moulds to improve production speed and reduce waste. 

The colour; although, I could add pigment to colour the part, the extra cost and lack of visibility of the part discourages me from going to this effort.

I am yet to determine its lifespan/durability.

The answer is no they are not the same, but they do serve the same purpose.

They are both used in conjunction with a split pin (cotter pin) to prevent loosening. Used in both low torque situations, e.g. trailer wheel axles, or on critical components where coming loose is not an option e.g. axle nuts on motorcycles.

The difference between the two nuts is the height of the nut. Castle nuts are taller than slot nuts for the same given thread size.

If you can imagine a standard nut with slots cut to approx. 1/3 depth of the nut then you have a Slot nut.
A Castle nut is more of a standard nut with the slotted section "tacked" on the top.

Castle nuts also often have the slotted section of the nut rounded so that a split pin can be confined to closer margins of the nut itself.

The nut can be either tightened to its correct torque and then a hole drilled radially though the shaft and a split pin used to prevent further rotation or in the case of a shaft with a predrilled hole, the nut is tightened to the correct torque and then adjusted slightly so that a slot on the nut aligns with the hole in the shaft. As is the case with trailer wheel nuts.

 Slot Nut                                     Castle Nut

ISO screws are usually marked with a small indent in the head just near the cross drive recess. As can be seen in the image below.

Using a Phillips screwdriver on a JIS screw is likely to cause damage to the cross recess as the Phillips driver will bottom out in a JIS screw before the side flanks have engaged fully. Screwdrivers ground purely for JIS screws seem to be no longer available, however there can be found screwdrivers that are ground to suit both Phillips and JIS. Search the web using JIS screwdriver and several will turn up. i have borrowed my daughter's JIS screwdrivers a few times and can definitely recommend them over the use of Phillips drivers for our JIS friends.

Anyway, I digress.

What I did find on my 1967 Suzuki was a few daggy looking M5 Pan head screws. No problems I will just replace them with some shiny new ones, or so I thought. My replacement screws would start to go in and then jamb up after a couple of turns. A quick check revealed that the pitch of the old M5 screw was 0.9mm and the replacement ISO screw  is 0.8mm. This lead me on a path of investigation that revealed that the Japanese did not adopt the ISO thread pitches until around about April 1967. My bike was obviously pre April 67. 

Finding these course pitch screws is near on impossible so I suggest you treat your existing screws with care.

I have listed below the details of the thread pitches. I hope this helps you out understanding what may be going on with your older bike.

Pre Apr 1967 JIS

3mm.....0.6
4mm.....0.75
5mm.....0.9
6mm….. 1.0
8mm.....1.00
10mm...1.25
12mm...1.5

Post Apr 1967 ISO

3mm.....0.5
4mm.....0.7
5mm.....0.8
6mm… ..1.0
8mm.....1.25
10mm...1.5
12mm...1.25

See also Honda Service Bulletin

Thread galling occurs during installation when friction and pressure causes the seizing of threads. Light seizing increases the torque required to turn the bolt often resulting in an assembly that may feel (or measured using a torque wrench) adequately tightened when in fact proper bolt stretch has not been achieved. This can result in failure of the joint to remain secure when in use. 

Excessive galling can also cause the fastener assembly to completely seize such that the bolt has to be cut or the nut split to allow removal. 

Materials susceptible to galling. 

Stainless steel, aluminium and titanium are the materials most prone to galling. Fasteners with fine or damaged thread are also more likely to exhibit the problem. Hardened steel bolts, especially when zinc plated, rarely gall. 

What Is Actually Happening? 

Thread surfaces have microscopic high points that can rub together during fastening. In most cases this does not present a problem as the points slide over each other without damage. 

Under certain conditions however, the surfaces will not slide past each other. The high points will then shear and lock together, greatly increasing friction and heat. As tightening continues the increased pressure results in more material being sheared off the threads. This cycle continues with even more shearing and locking until the threads are destroyed and the fastener will no longer turn in either direction. 

How to prevent galling 

Slow the speed of installation. 

Generation of heat increases friction and increases the chance of galling. It is recommended that stainless steel fasteners are installed without the use of power tools. 

Do not use bolts to pull the joint together. 

Using bolts to pull the joint together increases the heat generated in the fastener that leads to increased likely hood of galling. Use a clamp to pull parts together before bolting when possible. 

Use a lubricant. 

The use of a lubricant dramatically reduces galling and is the number one recommended method to overcome this problem. 

A nickel based anti-seize lubricant is recommended for use with stainless steel. 

The use of something like WD-40 or even a thread locking agent can also reduce friction and prevent galling. 

The use of a Copper based anti-seize is NOT recommended with stainless steel. Copper is more noble than stainless steel and will cause corrosion of the stainless steel possibly causing the joint to seize over time and prevent its removal. 

We strongly recommend the use of Nickel based anti-seize when using stainless steel fasteners. 

Do not use fasteners with damaged or dirty threads. 

Damaged or dirty threads will cause increased friction and therefore heat during installation increasing the chance of galling. 

Nylon insert or prevailing torque nuts. 

Use extra care when using these nuts and slow down installation to allow time for heat generated when installing to dissipate. 

If a fastener begins to bind STOP! 

Wait a minute or two for the fastener to cool, then back it off check for dirty threads and consider discarding the nut and start again with additional lubricant.