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HDG Bolting Oversize allowance for Nuts in metric type

HDG Bolting Oversize allowance for Nuts in metric type

(OP)
Hi There,

I saw a thread "HDG Bolting Thread Sizing Practice" where there's a guideline in ASTM A563 for oversizing nut size to give allowance for the HDG coating on the studs.However, A563 only indicates thread sizes in inch. May I know where can I get the metric type oversize tapped hole size?

Thank you in advance.

Regards,
Celina

RE: HDG Bolting Oversize allowance for Nuts in metric type

ASTM A563M is the metric version of this standard. Alternatively, ISO 965-4 and 965-5 are the International standards that pertain to hot dip galvanized external and internal threads.

RE: HDG Bolting Oversize allowance for Nuts in metric type

(OP)
Thanks TVP, I did not look into A563M previously. Are the oversize thread allowances (both metric and inch) applicable to be used on coarse and fine thread type? Example,

- Coarse thread UNC 1-8" pitch diameter = 0.9188 inch
- Fine thread UNF 1-8" pitch diameter = 0.9459 inch
Both coarse and fine thread above will have new pitch diameter per ASTM A563 (min: 0.9428inch; max 0.9516inch)?

Also, ASTM A563 indicates the diametral allowance for each thread sizes as well. May I know what is the difference between the diametral allowance vs. Pitch diameter (min & max) indicated on Table 5 of ASTM A563?

Thank you.

Regards,
Celina

RE: HDG Bolting Oversize allowance for Nuts in metric type

(OP)
To be clear on my question, my client require HDG coating for:
- A193 B7M(M16 stud size) coupled with A194 2HM (M16 nut size)
- A193 B7M(UN 1 1/2 stud size) coupled with A194 2HM(UN 1 1/2 nut size)

To fit the above stud and nuts into my machining parts, I have to design the tapped hole same size as the oversize nut per ASTM A563 (for inch) and ASTM A563M (for metric).

Questions:
1. Am I correct to say that for inch thread (ASTM A563):
- the required minor diameter = standard minor diameter + diametral allowance ?
- the required major diameter = standard major diameter + diametral allowance ?
- pitch diameter follow Table 5 of ASTM A563 ?
2. For the metric equivalent (A563M), it only provides the diametral allowance. How do I get the pitch diameter details for metric thread ?

Thank you.

Regards,
Celina

RE: HDG Bolting Oversize allowance for Nuts in metric type

The allowances are applicable to coarse and fine pitch threads.

The pitch diameters will NOT be the same for coarse and fine pitch, look at Table 5 (e.g. 1.125-8 and 1.125-7 are different).

The diametral allowance is the extra size along the thread diameter to allow for the thicker coating. The amount of steel in the fastener is reduced to allow this extra coating thickness. The pitch diameter is the actual diameter of the fastener threads.

Your equations are correct for minor and major diameters, see Note A of Table 5.

To get pitch diameter details, go to ASME B1.13M or ISO 965-4 & -5.

RE: HDG Bolting Oversize allowance for Nuts in metric type

Just to add to what CoryPad wrote, the pitch dimensions according to ISO 965-5 for M16 with tolerance class 6AX (same 420 μm deviation as ASTM A563M): 15.333 maximum and 15.121 minimum. The minor diameter is 14.630 max to 14.255 min.
 

RE: HDG Bolting Oversize allowance for Nuts in metric type

(OP)
Thanks All. The info is very helpful.

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