Well, quick answer is no. They are not the same and they are not interchangeable, although they can work under certain circumstances. The most important part is understanding the meaning of M8 and 5/16 to refer to the size of a metric screw or bolt, so then we can see why they aren't the same thing!
Is M8 bolt same as 8mm?
M8 is not exactly 8mm but it is sufficient from a non-engineering point of view as long as the thread pitch is correct. Luckily, most commonly available metric bolts have the same pitch. Regarding tolerance for common uses it can also often be ignored.
What is the size of M8 bolt?
Size Clearance Hole mm Tapping Drill (std Pitch)
---- ----------------- -------------------------
M6 6.5 5.0 mm
M8 9 6.75 mm
M10 11 8.5 mm
M12 14 10.25 mm
Metric Coarse Metric Fine BSF/BSW
------------- ----------- -------
M6 x 1 M6 x 0.75 1/4"
M8 x 1.25 M8 x 1 5/16"
M10 x 1.5 M10 x 1.25 3/8"
M12 x 1.75 M12 x 1.25 1/2"
What does M8 25 mean?
8 means 8mm nominal diameter (the thread will be less than 8 mm at the widest point) X 1.25 means 1.25 mm per thread (thanks the standard coarse pitch for this thread)Nov 9, 2020
What does the M mean in screw size?
The standard metric rack screw is called M6 x 1. The 'M' means it's metric. The '6' is the outside diameter measured in millimeters, and the '1' is the distance between adjacent threads, also in millimeters. Metric threads are used outside of the USA, and commonly in products by HP and other global entities.Apr 24, 2018
What does M8 size mean?
Hole Sizes for Metric Bolts The defined diameter of metric bolts is actually slightly larger than the actual diameter of the bolt shaft. So an M8 bolt would have a shaft diameter that's slightly under 8mm which means that the bolt should fit through an 8mm hole.Jun 19, 2020
What does M mean on a bolt head?
Fortunately, metric bolts are marked differently than SAE bolts. An ISO metric bolt larger than 6 mm in diameter has either "ISO M" or "M" embossed on top of the head. ... The number has nothing to do with the size, but does indicate the relative strength of the bolt. The higher the number, the stronger the bolt.
What size are M8 bolts?
Size Clearance Hole mm Tapping Drill (std Pitch)
---- ----------------- -------------------------
M5 5.5 4.2 mm
M6 6.5 5.0 mm
M8 9 6.75 mm
M10 11 8.5 mm