Metric bolt size question

[Kenny202]

Got to order some replacement bolts. they are metric. Bit confused about the thread size? To me they look the equivalent to a 5/16 bolt, which I would normally say was 8mm. Put my verniers across the thread diameter and about 8mm. But when I get a socket from my kit it's a 12mm that fits the hex head? So what size do I order? Is the socket size not the thread size....socket size size across the hex head?

[DaLa]

As long as you are certain they are metric.  Otherwise that's only part of the equation. You have to know the thread pitch, otherwise you'll end up stripping the female .  ( That isn't meant to sound exciting ).

[Kenny202]

26 minutes ago, DaLa said:

As long as you are certain they are metric.  Otherwise that's only part of the equation. You have to know the thread pitch, otherwise you'll end up stripping the female .  ( That isn't meant to sound exciting ).

So you don't know? They are metric

 

[sometimewoodworker]

35 minutes ago, Kenny202 said:

Got to order some replacement bolts. they are metric. Bit confused about the thread size? To me they look the equivalent to a 5/16 bolt, which I would normally say was 8mm. Put my verniers across the thread diameter and about 8mm. But when I get a socket from my kit it's a 12mm that fits the hex head? So what size do I order? Is the socket size not the thread size....socket size size across the hex head?

Bolt or nut AF size is never the thread size with metric fittings. Since the M6, M8, M10, etc apply to the OD of the threads which are slightly less than the M size, my M8 socket cap screws have a 7.9mm OD. The nuts that are used vary in AF dimensions depending on the material they are made from and the design specifications.

 

For  ordering it’s always the thread size, length to the underside of the head, and if you need bolts (Partial thread ) or machine screws (Fully threaded) And the head design, hex, slotted, socket cap, etc

 

But I usually go into Thai Watsadu and get them from stock. ???? It’s a lot easier.

Edited July 21, 2020 by sometimewoodworker

[Bangkokhatter]

You want 8mm bolts, as said above socket size can vary these days and for 8mm bolts it will be 12 or 13mm socket or spanner.

[Artisi]

Head for the local major hardware store, or the local "we have everything" mum and pop corner store, if they dont have they will probably point you in the direction. 

[rvaviator]

Not wanting to possibly confuse you even more ...  What are you bolting together? .. You may want to check the grade of the bolt - What was the old bolt holding together?

 

 

The common metric grade is 8.8 (just for any old thing you bolt together) ... anything more 'critical' .. 10.9 or 12.9 is what you should ask for - The number is embossed on the bolt head

[Artisi]

Order bolt diameter 8 mm. 

[shaemus]

On 7/21/2020 at 2:43 PM, Kenny202 said:

Got to order some replacement bolts. they are metric. Bit confused about the thread size? To me they look the equivalent to a 5/16 bolt, which I would normally say was 8mm. Put my verniers across the thread diameter and about 8mm. But when I get a socket from my kit it's a 12mm that fits the hex head? So what size do I order? Is the socket size not the thread size....socket size size across the hex head?

its really about the thread pitch.

 

example, i am always looking for HDG bolts for external use. I came across some M10's, i didn't look at the thread pitch as i assumed it would be standard 1.5mm. nope they were 1.0mm pitch.

 

not so much of an issue with imperial threads as the type of thread normally has a fixed pitch. Imperial will look a bit bigger and a larger angle compared to standard iso metric

 

there is plenty  of easy to understand info just a google away on thread identification. but pay attention to the material requirements of your workpiece i.e. dont mix incompatible metals and get the correct material grade if you require. there is normally info on the head of the bolt to help you assess the original.

 

Shaemus  

[canopy]

You need to think of it as there is no such thing as an M8 bolt. There are M8-1 and M8-1.25 bolts. Each type has totally different threads and don't fit each other. It is up to you to match the proper thread type on bolts, nuts, and fittings. This is a source of frustration because some consumer packaging in stores does not specify the thread type. Nor do a lot of online sources. It matters and different thread sizes in the metric line are common. For M12 there are actually 4 different thread sizes out there: M12-1, M12-1.25, M12-1.5, and M12-1.75.

 

[sometimewoodworker]

7 hours ago, canopy said:

You need to think of it as there is no such thing as an M8 bolt. There are M8-1 and M8-1.25 bolts. Each type has totally different threads and don't fit each other. It is up to you to match the proper thread type on bolts, nuts, and fittings. This is a source of frustration because some consumer packaging in stores does not specify the thread type. Nor do a lot of online sources. It matters and different thread sizes in the metric line are common. For M12 there are actually 4 different thread sizes out there: M12-1, M12-1.25, M12-1.5, and M12-1.75.

 

While technically correct in practice you are wrong.

M8 are everywhere Metric Coarse Thread (-1.25)

as are M12 Metric Coarse Thread (-1.75)

The sizes that are easily and widely available are all Metric Coarse 

 

M5 0.80 M6 1.00 M8 1.25 M10 1.50 M12 1.75 M14 2.00 M16 2.00

 

 

to get Metric Fine Threads you need a specialist supplier and they are NOT a common item. Like the M7, M9, M11 sizes that are in the specifications that and not generally available.

[RichCor]

Was asked recently to place a newer large screen TV in an existing wallmount, but the owner had misplaced the four bolts that secures the backplate to the TV.  These wallmount kits typically come with a 'shoulder-sling' of vacuum packed M bolts in multiple sizes, lengths, along with spacers. I scoured multiple hardware stores looking for replacements and non were to be had.

 

After two weeks of looking I was just about to plunk down another 500-1000 baht to purchase a replacement wallmount kit (just to raid it for the bolts and spacers) when we luckily found a local installer had a hoard of leftover 'shoulder-sling' vacuum packed M bolts he'd been collecting over the years with only one size missing from the multiple sizes included.

 

So if you're ever looking for a variety of M sized bolts and can't find them elsewhere, check out what's packed in those TV wall mount kits.    

 

...Oh and once the new TV was mounted on the wall using the new bolts we found the missing bolts the next morning sitting in a small basket on the refrigerator, because yes of coarse that's the way it works when you're looking for lost items [grumble!].

[Mama Noodle]

Did op ever say what he was trying to bolt together? 
 

 

[sometimewoodworker]

34 minutes ago, RichCor said:

I scoured multiple hardware stores looking for replacements and non were to be had.

Thai Watsadu is the only shop I’ve found that always has a stock of galvanised metric nuts, machine screws and threaded rod, other places may have them but not in so many sizes.

[shaemus]

On 7/23/2020 at 7:07 AM, canopy said:

You need to think of it as there is no such thing as an M8 bolt. There are M8-1 and M8-1.25 bolts. Each type has totally different threads and don't fit each other. It is up to you to match the proper thread type on bolts, nuts, and fittings. This is a source of frustration because some consumer packaging in stores does not specify the thread type. Nor do a lot of online sources. It matters and different thread sizes in the metric line are common. For M12 there are actually 4 different thread sizes out there: M12-1, M12-1.25, M12-1.5, and M12-1.75.

 

No such thing as a metric bolt! The OD is measured in mm which is metric as is the thread pitch. 

 

Im my experience of buying these items from the large DIY stores is that there is a real hotch potch and mixture of metric and imperial and any attempt to locate a certain size is met with a blank stare as the imperial fractional sizes is  seemingly a dark art. 

 

As i mentioned above. I was looking for m10 HDG 1.5mm, came home with m10 BZP 1mm.

 

 

[daveAustin]

8mm bolt with AF 12mm head? mmm

Have you got dodgy Chinese-made sockets? 

 

[Don Mega]

15 minutes ago, daveAustin said:

8mm bolt with AF 12mm head? mmm

Have you got dodgy Chinese-made sockets? 

 

Very common in the automotive world, typically they will be JIS.

[thaibeachlovers]

Ah, the joys of the mechanical world. I bought loads of bolts, nuts and washers etc from auctions of businesses closing, but they can be of any type- Whitworth, AF or metric. Pity they couldn't standardise the hex part so we don't have to have 3 sorts of spanners and sockets.