Modern Vespa

At this point, I have all the necessary bits, even a magic unicorn set of JIS screwdrivers that are not sold in retail stores and had to be purchased online.

Back to the OP's point though, theoretically, could one just replace all the fasteners on the Vespa with one head-type? Is there any functional reason they are all different? I'm thinking Torx would be the best option for an all-around fastener as it can probably be used for all connections and doesn't strip easily. Why doesn't Piaggio just help us all out and standardize everything? I'm sure it's because of the now Global production of the Vespa, but it's a PIA...[/i]

In addition to the security screws described in the above posts, there are adjustment screws in small carburetors such as those used on chain saws and weed whippers that are designed so that the average homeowner cannot adjust them and create more pollution. This would be ok except that the gas to air ratio of these small engines seem to become leaner over the years until the engine no longer runs.

I think it's a plot to force you to return the engine to an approved repair facility instead of adjusting it yourself, but the adjustment tools are easy to get from China.

Cheers,
Bob

Another type of conspiracy is to have everyone switch to the metric system by confusing with the head types.

Yes, I know, this is becoming an obsession. So, I've been digging through the parts diagram and am not understanding the way it is sizing the screws. I'm used to diameter, thread pitch, and length. Or numerics for woodscrews by length. Here are some examples from the diagrams that I can't figure out:

Screw d4,2x16
Screw d3,5x9,5
Self tapping screw D4x13
Screw M4,2x13

I'm fairly sure that 4,2 is 4.2 in the US. But maybe not, because what screw is sized 4.2 of anything?

What is the difference between something labeled 'screw d4,2x16', something labeled 'self tapping screw 4,2x16', and something labeled 'screw M4,2x13'

Anybody able to help translating?

If I had to guess, I would guess that d4,2x16 is a screw whose diameter is 4.2mm and whose length is 16mm.

Do you have the parts diagram where that came from?

M4 is a standard Metric size. It does mean (roughly) 4mm diameter, but the technical name is M4.

M4.2 is... well, that's maybe stretching the definition a bit, but not sure if that's a euphemism or a real size.

I was looking at the screw descriptions on pages 34 - 37 of https://www.af1racing.com/ProdImages/st3/EVG6000US2.pdf

Could it be that 'screw' has one set pitch,
'self-tapping screw' a different set pitch, and
'M' another different set pitch.

I thought maybe it was something so well known in Italy that it didn't even need to be written down. Thread pitch is what is making my head stutter.

IME, a screw or bolt labeled M4 (or M6, M8, etc) is a metric machine screw. It does not specify the pitch of the thread, though generally each Mx screw will typically only show up in one or two different pitches. The Pitch is often specified together, e.g. M6x1.0. In that case, the 1.0 refers to a thread pitch of 1.0mm. You have to kind of do some interpretation based on the size of that second number to determine if they are talking about thread pitch or length. You wouldn't typically find an M6 screw that was only 1.0mm long, so it's clearly specifying pitch in that case.

You might also see M6x1.0x20 (or some such) which would mean M6 (diameter of 6mm) with 1.0mm thread pitch and a length of 20mm.

My guess is the ones labeled "d4,2" are not machine screws, and thus don't use the M designator. They are almost certainly sheet metal screws, or self-tapping screws. The distinction starts to get blurry after you get away from machine screws, so don't read TOO much into it.

I'm going outside to retrieve one of the screws in the diagram to show you. Be right back.

Going from the parts diagram below, and looking specifically at the screw labeled "6", the legend says it is d4,2x16, which implies a 4.2mm diameter screw with a length of 16mm. It is in fact 4.2mm in diameter (see subsequent photo) but the length is actually 25mm. It's definitely the screw referenced in the diagram, though, so unless it's changed since 2010 (the GTS it came off of) the diagram is wrong.

And that's pretty typical. The only way to know for sure is to remove the screw and measure it. The diagram isn't as definitive as you would hope.

I took out the screw labeled "4" in the diagram. Voila! It is 16mm. So either my bike is built wrong, or I swapped it, or... who knows.

They are similar screws, but not identical. In practice, though, either one clearly works in the other position. Sheet metal screws are pretty forgiving. The only thing to be careful of is puncturing hoses with a screw that is too long.

A screw labeled "M4", though, MUST have the correct thread pitch, no exceptions.

Thanks Jess for measuring all that. Maybe instead of trying to copy out all the screw sizes I'll just buy a set of calipers. A good set too, so I can even measure the thread. My wife will love it.

https://www.gberardi.com/info-tecniche/estratto-uni-6946/

Extract UNI 6946. Diameter of pre-drilled holes for self-tapping screws

BTW, Widia is derived from "wie Diamant" = like diamond

Love your Mitutoyo, jess.
I have a Mitutoyo with a "Nonius" instead of a dial. Had to look that up. It's called Vernier scale in English according to wikipedia. One of those inventions that just fascinate me.

There is a more precise (and subjectively easier) way to measure the length of a screw without the head.

Not the same quality, but I think good enough for my purposes. Plus it has both Metric and SAE
http://www.anytimesale.com/DUAL-Reading-Dial-CALIPER-METRIC-Standard-Inch-mm-p/203185.htm

Calipers are a great tool to have around, but probably not the right tool for thread pitch. For that, you need something like this gauge set. There are others like it, but this one is fairly reasonably priced.

Vernier scale calipers appeal to the clever side of my brain, as they are one of the cleverest inventions in history. That said, dial calipers are much easier to read.

I have a nice vernier caliper that is made specifically to scribe lines in metal at an extremely accurate offset from the edge, but I generally don't reach for them to actually measure anything. That's a good tip!

That will work nicely, I think.

The caliper is one of the measuring tools that must be in the small home workshop as well as a metal tape measure, a tire pressure gauge, a small but simple tester and a small spirit level.

In my work shop, a shot glass with bourbon measures my spirit level

I do have a set of Whitworth wrenches for my old MG.

I have some pretty cool tools at my disposal. Calipers up to and including these 24" Mitutoyos, my trusty 52x80x40 Mitutoyo CMM and my Hexagon RS6 laser scanner, both running PolyWorks. Just for giggles I brought that Stella clutch cover in and performed a full layout, just to make sure the new one was the same. Of course they weren't.

It only works with the glass horizontally and the drinker in a vertical position ... Absolutely yes, otherwise it wouldn't be a real british car.

I've got tool envy. Not that I have any reason to have them of course. Just, general jealousy.