# Problems understanding imperial hole sizes

1. Oct 6, 2009

### Chris_N

We need to manufacture a structural component, but we do not understand the imperial hole dimensions given on the drawing:(we went metric in South Africa in the 1960's)

5/8"x29/16"-1/8"

We think it may describe the bolt and not the hole, but are unsure what it means.
Can anybody help?

2. Oct 6, 2009

### FredGarvin

Is that for a clearance hole? That call out makes no sense. Please describe the hole function and where it is on the part. I'm sure we can decipher it.

If it is a clearance hole, perhaps, since $$\frac{29}{16} + \frac{1}{8} = 1 \frac{15}{16}$$
that they mean simply a 5/8 diameter hole by 1-15/16 deep. I'm really reaching there. More info would really help.

3. Oct 6, 2009

### pantaz

Perhaps the -1/8" indicates a tolerance range (+0/-0.125)?

4. Oct 7, 2009

### Chris_N

The hole is to be punched through an unequal angle 64mm x76 mm x 6mm (Electrical substation structure being maintained) .

We think the dimension refers to the bolt, namely:

5/8" (diameter) x 29/16" (length) - 1/8" (Pitch?) and that a generic tolerance on the hole is applied.

Does this make sense?

5. Oct 7, 2009

### pantaz

Standard thread pitch for 5/8" diameter fasteners is 11 tpi, or 18 tpi (threads per inch). Less common is 24 tpi.

I believe the -1/8" spec is a tolerance for the bolt length.

6. Oct 7, 2009

### gmax137

Maybe the 29/16 is really 2 9/16 ie, two and nine 16ths inch. Why anyone would write 29/16 instead of 1 13/16 is beyond me.

as for the overall question, I have no idea. 2 9/16 inch would be 2.5625 inch or 65.0875mm; maybe that corresponds to your 64 mm? (I mean 64 mm to the nearest 1/16 inch)

7. Oct 7, 2009

### FredGarvin

Is there any way that you can scan in the print section that has the hole call out? It would sure help. I definitely like the idea of the .125 being a thread length tolerance call out although it follows no drawing standard I have ever seen.

There are a few things that worry me about the callout:
1) If it is a clearance hole for a 5/8-11 or 5/8-18, then a 5/8 diameter hole will be too small for a clearance hole.
2) If you take the -.125" for the bolt length tolerance, then the bolt will not be long enough for the angle. Even with the full length, there is no room for a nut.
3) If the hole is going through a piece of angle, why do you need a hole that deep? You should only need a depth equal to the thickness of the section, i.e. 6 mm.

This is why it would be nice to know exactly waht is going on around this callout.

Last edited: Oct 7, 2009