Bolt thread size

I'm ordering some items from ebay China. The bolt thread size is listed as 8mm/0.31. Looking at my tap & die set I have 2 for 8mm, a 1.0 and 1.25. They are listed as 8mm-1.0 and 8mm-1.25. Is the 8mm/0.31 one of these or a new one I'll have to order?

The .31 is bolt diameter
1.00 and 1.25 is going to be thread pitch :ie: course or fine

Millimeters to Inches (mm to in) conversion calculator

Beware of China made bolts....most are not very strong

Here's what I'm ordering, going to spend a few days on the coast and want to catch some flounder.
5-Prong Fishing Fish Frog Eel Salmon Barbed Spear Gig With Long Nut A1 | eBay
The nut size is listed as 8mm, when I sent a contact the reply was 8mm/0.31.
I sent another contact asking for the thread pitch.

Here is a better place to buy metric bolts and nuts. I've bought a lot of them for my motorcycle. https://www.boltdepot.com/Default.aspx

Jimmy, that's kinda over kill for flounder gigging. Just get you an old fashioned frog gig. Speer him and hold to the bottom. Slide your hand under him and pick up so he dosnt slide off. Put many a pound of them in the tub with one.

I have 5 of these ordered @ $3.39, they are stainless steel.
I have some 7/16" rod that is tapped 8m-1.0. I have a lot of bamboo that the rod can be inserted at one end for a 5 or 6 ft gig rod.

Sorry ,I don't know very much about thread pitch.

Was the reply I got this morning, Lordy.

Here is one thing I have found in regards to metric bolts coming from Asia (specifically China). In some instances, they are NOT exactly what we would consider an 8mm or 10mm.

I owned a chinese tractor for a few years. When I purchased it new, the owner of the business told me specifically that you cannot simply go down to the hardware and purchase a 14mm bolt. It will not fit and will not work. The threads are slightly different, the pitch slightly different, heck, event the size is slightly different.

What I did however find was that I could find the next largest step up in bolt and the identical tap to it and tap the existing hole. I would then purchase newer, high quality, higher tolerance bolts to work and fit better.

I'm guessing that this is what you will find with these. A standard 8mm hardware bolt will not fit or thread properly.

My son has a tractor like that. Back woods metric threads aren't the same as improved metric threads. It has a front end loader, had the cylinders rebuilt here, but had to order the hoses. A banjo bolt broke, that took a while to find and ship.

I call them NKE bolts...

North Korean Engineering!

In another forum a member posted a link for metric threads. Looking for bolts/nuts we find a fine and course at most stores. There are 5 different thread pitches for an 8mm bolt on this chart. 8mm-1.25 is listed as an 8mm.
METRIC THREAD -- EXTENDED THREAD SIZE RANGE

Yesterday I got everything set up to drill/tap these aluminum rods my son gave me years ago. Suppose to be 7/16" dia, which would leave very little wall after tapping 8mm. I dug through my stash to find them. I look at the ends, thinking these aren't 7/16", they are 3/8". 8mm is 0.315, 3/8" is 0.375 which will leave 0.060 for the wall, 0.030 per side if centered correctly.
Now look to see what I can find, maybe 1/2".

:crazy:

You would need at least 1/2 rod to Drill and tap any 8mm hole.
8mmx1.25 is standard and should be drilled with 17/64th t0 7mm drill. If doing by hand I recommend the 17/64th. for an 8mmx1 thread you would use a j drill - 9/32nd. You might be able to take it to a local machine shop and they can help. They also would be able to tell you what pitch you have. and maybe drill and tap it for you for a small fee since it is only a couple of holes. Good luck.