Metric Carriage bolts?

Anyone out there know of a source for metric carriage bolts? I need some longer bolts to attach my Thule Cargo box to a non Thule rack. I’ve found a few sources on-line but they all have 1000 bolt minimum orders.

I need to stay metric so they fit properly into the molding on the Thule box.

Why carraige bolts?

– Last Updated: Mar-26-09 1:35 PM EST –

How about using normal bolts instead? You can get regular bolts in metric sizes at any decent hardware store. It's hard to imagine why it would matter, but IF it is extremely important to NOT have a protruding head, grind each hex head so that it tapers to the edges. Presto!

Hardware store
I dont know what its like up there, but in my neck of the woods we have a farm supply that has a guy come in each week to refill all those little drawers of oddball stuff.If you find a store like that maybe you could leave one there for them to compair it with.

Metrics are a serious pain in the…funnybone, because of the size.threads per???,and thread pitch.

If you dont have a store like that,just forget I even sent this.Or try a buddy that works maint. at a factory.

Here’s another thought
You said you wanted to stay with metric to fit the molding, but didn’t say anything about the nut. That seems to imply you are looking for a particular diameter rather than matching threads. In that case, use whatever you can find. Bolt diameters need not be all that precise. Get whatever is close and it will work as well as anything that is “proper”.

metric bolts
I’d ask you local hardware store. Make sure to order a metric Crescent wrench so you can get 'em tight.

I assume
that the reason you need a metric carriage bolt is because the size of the square under the head is different on a metric vs. standard carriage bolt, and you need that square to fit into a slot in the thule box.

Try McMaster Carr. ( When I’ve had to order hardware from them before it didn’t come in unreasonable quantities. For something like long carriage bolts I’d be suprised if a box had more than 20.

McMaster Carr

I suspect that they do not have metric bolts of this flavor. Replacing the cheesy bolts that come with Thules with a good quality SAE plated bolt might be a good option.


can you drill out metric and retap for SAE threads ? Metric can be hard to find right size …Lowe’s stores have some metric selection. usually only only the best stocked hardware stores carry a large selection of sizes.

southern hardware
just off of Wilkerson rd has a great selection of metrics, as do many manufacturesrs. If you can give me the metric size I may have something around here I could send you.


denver NC

The imperial bolt doesn’t fit into the molded slot quite right, so I would prefer the metric. I’d like to have something the fits exactly if it’s securing a large cargo box to the roof.

Thanks for the responses everybody.

Small quantity/online order
Lots of companies have these, but not to many seem to have one ordering for single/small order. Try link below for one. They show M5 through M12 carriage bolts at various lengths.

Copy/paste whole link or just scroll down. Metric are mid-page between standard and brass. If you try to buy there, be sure to enter quantity AND check the box before clicking “Add to cart”. Bolts are cheap, shipping not so at $8.

Thanks Greyak!

No minimum order
I once ordered a few oddball bolts from McMaster-Carr. They had NO minimum order, and I got the stuff in two days. They and Lee Valley are the motherlode! Oh, and Newfound Boatworks is pretty good, too.

Solution found!

– Last Updated: Nov-11-09 9:34 AM EST –

Thule makes longer metric carriage bolts! It's the Thule Xadapt 6 kit, they are long enough to attach my cargo box to the (almost 2" thick) Trac Rac cross bars.
I bought them from
They were extremely helpful, they actually measured the bolts for me.
Why Thule doesn't know they make longer bolts is a mystery but at least one of their resellers has a clue.
None of the suppliers suggested had long enough bolts, or they were out of stock.
Talk about responding to a long dead thread :-)

same proublem
this is a old thread. I seam to have the same proublem. I got some j cradles I want to install in my roof rack. The carraige bolts are 8 x 12.5mm and I need some that around 100 mm long. I sure hate metric. just spent and hour on google and can’t find any.

any thoughts.


bolt woes
I’m in the same… heh… boat. Rack bolts are just a little to dang short. Grrr.