Modern Vespa

Thanks, but I think Shoulder Bolts are only threaded at one (the inserting) end; I think I'll stick to the threaded rod & coupler device, which I should be able to tweak for the correct length and then "lock" in place.

SO.... I got the metric measuring tool. Woohoo!
Checked the threads on the Short Standoff (the assumption being that they're the same as the Long Standoff's).
Good News: It's M6.
Bad News: I swear they are pitched at 1.25.
Will go and have a "professional" measure it again... maybe it's my 72-year-old eyes?
!!!!!!
Help me Obi-Wan..., you're my only hope...

Got any M6 nuts lying around? Would be a simple go/no go check.

They're not.

I think one of the ISO standards like 9001 or something standardized this, so you aren't going to find the weird sizes like you used to.

Are you forgetting who we're dealing with here?

I'm on my way to a hardware store to check!

Some closure...Yay!
The M6 is pitched at 1.0. See attached from Home Depot
This green-lights construction of a Long Stand-Off after we get the old broken-off stub out of the frame. Of course, my Home Depot doesn't have the needed pieces.
Baby steps...

Have you found a left twist drill bit? Otherwise standard drill & easy-out.

OFG

Not locally, but I'm asking my Vespa Dealer to do it for me.

Harbor Freight have LH drill bits.

Plan B.. nice to know. But since the scoot was going in anyway for its 600...I'll let it be "serviced".

From ~ $25 of Amazon parts:
60mm M6 Hex Rod Coupler Nut
5.4mm M6 Locking Nut or two
60mm All-thread M6 Rod
I should be able to create a ~ 95mm replica of a Long Standoff with room for adjusting. Maybe a bit of Loctite?
With many spare bits to build more - bwahaha, "Made it Ma, Top of the World!"
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I'll take a picture when it's done.
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Did I miss anything?

$25???? I hope you meant $2.50, even at Ace hardware prices.

Note, I never mind paying Ace well over the top for nuts, bolts and screws - I could never afford to keep such an inventory.

I'm not totally sure what your vision here is, but this stood out: I don't think you need a coupler nut -- I think you need a spacer (unthreaded inside) with an M6 bolt passing through it.

But maybe you had a different plan and I just haven't quite absorbed it yet.

Can I also add that these bolts for the rack don't need to be fitted that tight and also check the front rack holes fit over these 3 bolts well. My rack holes needed to be drilled out a bit as some where off centre and this caused one of my GTS300 rack bolts to shear on the threaded part. So to reduce the stress on these don't overtighten and make sure the rack holes line up. FYI the rack was original vespa.

That's for 6 rods, 6 couplers, and 25 nuts - if Ace has fewer for less I'll find out today - thanks!

Here's my thinking:
The original Long Stand-Off is ~ 90mm long, with a deep 6mm screw hole at its end].
If I screw half of a 60mm bolt into a 60mm coupler (locked in place with a nut), I will have a ~ 90mm device with a ~ 30mm hole at one end to screw in the Short Stand-Off (which was a 15mm screw at its end) and a ~ 25mm screw to go into the frame bracket (accounting for the locknut) at the other end.
The head of the coupler needs to extend ~ 5mm outside the leg shield frame
The ~ 25mm bolt length going into the frame bracket I will also locknut to secure, if possible.
There's room for fine-tuning this.

Good suggestion, thanks!

Update:
3 M6 Locking Nuts from ACE $2.85 - Save $3 over Amazon
1 M6 100mm Threaded Rod from ACE $2.95 - cut in half to make 2 50mm rods - save $5 over Amazon
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M6 60mm Coupler Nut- ACE (mine) doesn't carry other than a very short one - may need Amazon for this (@ $11 for 6).

No Home Depot or Lowes nearby?

Yes, have both - but neither carries M6 long coupler nuts *sigh*.
eBay has them in brass or aluminum from China with 2-week shipping costing almost what Amazon wants for 6 with next-day delivery... may have to give in.

Got it. Does the coupler nut fit inside the hole in the frame? I can't remember, was it 12mm?

Yes, the coupler is 10mm Hex, so it will pass through the 12mm hole in the frame - I can live without the 13mm head the original standoffs use. I may use some rubber tubing to reduce "rattle".

Are you sure about that? It's not the flats that matter in measuring the effective diameter of the coupler nut, which is what the 10mm specifies. You have to measure the distance between opposing points.

No, I'm not sure... there are round couplers I may need to consider (no points!). Could grind down the edges... if I ever get one.
Or does someone know this information?
Or a redesign - a longer threaded rod (80MM) with a shorter round (30MM) coupler - 15MM inserted should give a 95MM replacement. Add some locknuts, of course.
SO DAMN CLOSE!

I hunted down an ISO document that specifies nut dimensions. An M6 nut with 10mm flats should be just over 11mm, so you're good.

https://www.wermac.org/bolts/dimensions_hex-nuts_across-flats-and-heights_din-iso.html

YES, as I proved last night! See attached. That's my M6 Lock Nut (which is sized at 10MM, see attached) going through the 12MM hole of my Metric Measurer, which I just happen to have. I have to assume the Coupler 10MM Nut is spec'd the same.
*Damn the torpedoes, FULL SPEED AHEAD!!

THis solution would be the simplest one but also requires some delicate work i.e. if you over torqued the bolt the first time around, drilling and taking out the broken off bit can be a daunting task, but it can sue be done. Just take your time and do it slowly. You can find spacers/standoffs on places like Mcmaster Carr.

My dealership got the broken-off piece out easily and I get my scoot back tomorrow. Parts to build the new long (indestructible?) spacer will be ready for a nice weekend project. Progress photos will follow - THIS forum made this possible, as far as I'm concerned.

SEE THE FIX!
It's stronger than the original.
It's adjustable for a perfect fit.
There's 30MM of "locked" threaded rod inside the Coupler.
I had to buy some parts from Amazon; so you can stop the second-guessing about other probable or likely sources.
The Short Stand-Off fits perfectly.
It'll pass through the 12MM hole in the frame.
IT'S SHOWTIME!
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Again, my thanks to everyone who helped me get this far.

Well, I hope you at least used MV's associate link.

(Kidding!)

Now that you solved the problem, would you be kind enough to share what one may want to do if they run into a similar situation. Would be helpful to have not necessarily links for the parts as they could change in time but maybe the dimensions of the various parts that you got to solve the problem.
Thanks in advance, I am asking only cuz I have one of those carriers in the front and I know I could break that bolt too.

Happily: everything is M6 1.0 thread pitch (standard).
*3 M6 Locking Nuts from ACE. Amazon sells in bags of 25. Nooooo.
*uxcell M6x10x60mm Coupling Nuts - Galvanized Carbon Steel Hex Threaded Rod Coupler from Amazon - only comes in a 6-pack and I couldn't find them anywhere else. Fits through the 12mm frame hole.
*uxcell M6 x 60mm 304 Stainless Steel Fully Threaded Rod a 10-pack - also from Amazon. Ace sells a 100mm length you could cut down, but I didn't want to fuss. 30mm of the 60mm rod goes into the coupler.
Coupler 60mm plus remaining rod end 30mm = 90mm total; what you want. The double nuts "fake" the bottom of the original spacer where it contacts the frame mount screw hole. The nuts allow you to adjust everything. You need a long coupler to have room for the Short Standoff to screw in its 15mm M6 screw.

The lock nuts are life savers; as I suspected adjustments had to be made AND the coupler has to be LOCKED to the rod or it'll unscrew if you try to remove the assembly (as I found out) to make the adjustments. Success is possible.

Nice work!

Note: the (cheap) Rack Clamp appears to likely eventually damage the chrome.
I've gone and covered it with a length of leftover bicycle inner tube - total protection.
AGAIN, thanks to MV.com and the community it supports for helping me get to this point in my Vespa adventure!

Well done, thanks for sharing how you solved the problem.

Though if one doesn't use the rack and wants to take it off, are there any covers available to plug the holes. My Vespa is a 2018 Touring edition and I bought it from a fellow MV member. I haven't used the front rack ever but I haven't taken it off either.

FYI: the original instruction call for protecting the finish with vasoline.
The holes are 12mm - it sounds like you want a plastic cannon plug dust cap of the appropriate size.

If you break the long bolt that hold the front rack in place on the new GTS HPE or GTV, and you don't want to fish through the metric section at Lowes to make your own, you can order one and call it a day. We also have the shorter one.

https://scooterpartsco.com/misc-c-801_3501/special-bolt-for-piaggio-oem-front-luggage-rack-p-37822.html