Help me understand bolt specs please.

[Wolkenflieger]

Hi All,

I stripped a bolt on my Shadow 2 Optic plate. The plate is from CZ Parts in the Czech Republic and is manufactured by CZ themselves. Unfortunately I used VibraTite (probably too much) and I could not get the bolt out without stripping it. Eventually I used an extraction kit and it worked beautifully, no damage.

I installed the optic bolts per CZ Parts torque recommendation, which is 1.3 Nm or 11.5 inch pounds, and I used a T10 torque-limiting driver.

I wrote to CZ Parts asking about the bolt sizes, and they are;

Torx M3x8; 8.8 ISO 14581

Can someone help me decipher this to find a replacement online? I need this for the buyer of my Shadow 2 and for future reference.

The M3 is probably diameter in mm. Easy enough. What is the 8 in M3x8? Normally I would expect the second number to be length or thread pitch. Thread pitch doesn't seem to match, so I'm guessing it's length as it looks about 8mm long.

What is 8.8? I don't see this number at all when I search for replacement bolts. If the above 8 is length then this must be thread pitch, but I don't see 8.8 as a spec on any bolts I've found online. It could be length too.

I Googled ISO 14581 and got this;

"ISO 14581 is an international standard that defines the characteristics of hexalobular socket countersunk flat head screws. These screws are made of steel or stainless steel, have metric coarse pitch threads, and are product grade A. They have a limited ultimate tensile load due to the head design and the hexalobular socket penetration, which is indicated by a specific marking"

So, it appears that ISO 14581 is also telling me the thread pitch, which is "coarse" in this case?

Any help is appreciated. Thank you!

 

[Wolkenflieger]

UPDATE

The kind folks at CZ Parts are so friendly and responsive. They deciphered the code for me;

As I suspected, M3 is diameter (easy enough). The 8 in M3x8 is length. The thread pitch is for metric bolts/screws at 0.5 or "coarse" per the ISO 14581 standard. The 8.8 number is strength, though I don't know what they mean, tensile? Shear? Hardness? Vendors seem not to show the strength number, but at least I know what it is now.

CZ Parts customer service is top notch, by the way! This is where I get all my optics plates.

 

[joefrank64k]

For imperial bolts, you’ll often hear ‘Grade 8’ as referring to very strong bolts.

For metric, ‘Grade 8.8’ are equivalent to imperial ‘Grade 5’. Strong, but not as strong as imperial G8.

Here’s a chart that I’ve found helpful:

 

[Wolkenflieger]

For imperial bolts, you’ll often hear ‘Grade 8’ as referring to very strong bolts.

For metric, ‘Grade 8.8’ are equivalent to imperial ‘Grade 5’. Strong, but not as strong as imperial G8.

Here’s a chart that I’ve found helpful:

Helpful, thank you!

 

[AR15barrels]

I keep M3x8mm long grade 12.9 flat head TORX drive screws on hand because so many people strip the allen drive sockets out and then bring me the slide for removal of the stripped-out screws.
Torx drive socket heads are harder to strip out than typical allen drive socket heads.

 

[Wolkenflieger]

I keep M3x8mm long grade 12.9 flat head TORX drive screws on hand because so many people strip the allen drive sockets out and then bring me the slide for removal of the stripped-out screws.
Torx drive socket heads are harder to strip out than typical allen drive socket heads.

Wise move! I kinda discovered this first hand!