nut and bolted terminology

[drainman]

i am a newby to building a cnc and i am making the jgro cnc but the terminology of the nut and bolts IEhex head bolt 1/4-20x3/4 is confusing me how can i revert the term into metric as i live in england

[i2i]

1/4 - 20 x 3/4

Sounds complicated, but all you have to do is break it down into the three parts.

1/4 = outside diameter of thread = 1/4" = 6.35mm
20 = the pitch of the thread 20 threads per inch
3/4 = the length of the thread = 3/4" = 19mm
Hex head, that's the shape of the bolt head which in this case is a cylindrical head that has a hexagonal hole for an allen key

If you're looking to replace the whole thing with metric, ie. if you're making it from scratch it would be 6mm x 20mm Hex head/cap head.

The original bolt is probably 1/4 unf x 3/4"


Edit, i've just noticed a few american sites are using "hex head" to describe a standard hexagonal bolt (six sided bolt head)

[Jonathan]

Edit, i've just noticed a few american sites are using "hex head" to describe a standard hexagonal bolt (six sided bolt head)

The type you use an allen key with is called socket head strictly speaking...

[deannos]

The type you use an allen key with is called socket head strictly speaking...

That's what i'm going to use, looks neater to me, more professional.

[Jonathan]

That's what i'm going to use, looks neater to me, more professional.

I agree, also the heads are stronger than phillips / slotted.

[Web Goblin]

Socket head screws are also called Cap screws as well. I find that the biggest benefit of using them is for access with tooling. You can get to them without the need for large spaces to fit a spanner and they can be counter sunk into your job as well. Just take care when tightening them up if you are using ball-end keys. I have snapped a few of them off inside the cap screw, particularly with cheaper tooling.

Regards

Ian

[Jonathan]

...they can be counter sunk into your job as well. Just take care when tightening them up if you are using ball-end keys. I have snapped a few of them off inside the cap screw, particularly with cheaper tooling...

Counterbored surely...:whistling:
I've never snapped a ball-end key in one, but I have often had the key get rounded off and stop working. When that happens I just grind off the end of the key to make it into a standard key.
I use socket head cap screws on everything, for the reasons you gave, except where the head is too high - then it has to be button head.

[Web Goblin]

Counterbored, ok I`ll give you that one. I had once snapped the ball end off a 12mm key trying to get a road wheel off a very old rusty shaft on a gas cutting machine. Ended up ordering a new wheel and shaft and cutting the shaft out with a gas torch. Right PITA it was too.

[drainman]

many thanks for all the answers and for taking time out to look at the problem