Thread identification

Often found on laptops, other computer equipment and cameras as well, but in such small sizes, and in the case of cameras often sealed with threadlock or paint, they are even easier to mangle.

For a long time, French cars, certainly Renaults, used a TACL screw head, a sort of enclosed diametral slot, with a small central female spigot. At least a narrowed thick conventional screwdriver would deal with those.

Then the continental motor industry started using Torx heads on cylinder head bolts..

To retain aftermarket exclusivity some manufacturers used really odd fixings. The governor shaft on the Bosch EPVE was retained by three sided fixings (Guess what was the only place you could buy a socket to fit? )

I came out of a meeting with a potential fastener supplier, having just said "Nothing special, we don't want five sided heads" to find a Japanese cartridge type injection pump with five sided heads!

Presumably all in the name of tamperproofing; or exclusivity?

Howard

It may well be apocryphal but I have heard it suggested that the reason the GPO used (in pre British Telecom days) 3/5/7/9 ba fixings rather that the more common even numbered ones was so that people didn't pinch the bolts etc

An urban myth? Probably!

The threads on japanese motorcycles are metric.

M4 x 0.7

M5 x 0.8

M6 x 1

M8 x 1.25

Anything above m8 will have either a 1mm or 1.25mm pitch.

The diameters of all threads will be a nominal size, so allowing for clearance/wear/damage etc a thread od not measuring a whole number will probably be the next highest whole number.

If you want to measure the pitch measure across the tops of 5 or more threads then divide the measurement by the number of threads.

This will be far to late for OP but anyone else looking for information may find it useful?

I worked in Honda dealers in late 70's, find the general information manual online, it fills in 'gaps' in factory service manuals. I've seen a lot of complaints about service manual not giving full details. It's because they were written for dealer staff, not someone with little experience or training

Japanese screws are JIS, correct screwdriver fits and doesn't bugger up the 'cross' (JIS = Japanese Industry Standard)

Google it for more information. It's been around since 1966 or so (previously there were different metric standards for threads, fit, etc) DIN may use same thread form but bolt head sizes are different

Honda use standard diameters but fine thread versions.

Finer pitch gives a larger core diameter plus ability to apply more torque

Usual pitches are 0.8mm, 1.0mm, 1.25 and 1.50mm irrespective of the diameter. (24x1.0 is actually quite common on steering stem as is 14x1 and 16x1 on crank ends)

1mm pitch is most common on 6mm and 7mm bolts but can be 'anywhere' (Honda normally use 7mm chain adjuster bolts on >250cc)

1.25mm pitch most common on 8 and 10mm engine bolts and clamp bolts (8mm standard ISO size)

1.50mm -, usually axle bolts

The only thread I found incredibly surprising was on spoked wheels where Honda were using 1/8" WHITWORTH until at least the late 1970's (Harley Davidson were using 3 or 4mm metric at the time,)

Comstar wheels were designed to flex but the rivets at rim will loosen over time (hell, they came loose while some bikes were still under guarantee)

A metric thread pitch gauge will be useful, I've had some since early 70's and haven't bought any new since early 80's

On a machining site I wouldn't have thought anyone wouldn't know how to measure any thread they saw?