Unknown Reference on Print "+H12, BS 1916, .002"

Hi and thank you in advance for any help.

I have a print and I am unfamiliar with a reference listed in the standard tolerance block. For "Drilled Holes and Machines Bores" it lists the following:

+H12
BS 1916
.002

I know there is a BS-1916 tolerance spec. but I ave never seen it and don't quite get this whole thing. Any insight would be greatly appreciated.

Thank you,
James

So H12 is an ISO tolerance, it gives an allowable tolerance based on the nominal diameter of your bore. You can google H12 Tolerances and get a chart. BS1916 seems to do the same, though I think you'd have to do some digging to get an actual copy of it without paying.

No idea where the .002 comes into play....

I'd be calling the customer and asking...

I've found a listing of the BS-1916 tolerances. H12 is for clearance.

Nominal definition is -0 to + X where X varies from + 0.004" for holes between 0.04" and 0.12" diameter to + 0.025" for holes between 15.75" and 19.69" diameter.

The 0.002" is almost certainly a bottom limit modifier. If so the smallest permissible hole size must be 0.002" over nominal i.e. tolerance becomes + 0.002" to + X where X is defined relative to hole diameter as above.

For practical purposes the hole size / tolerance relationship is the same as for ISO except for being in imperial rather than metric. Both BS 1916 and ISO standards are derived from the (now defunct) ISA standards.

PM me if you'd like me to photocopy relevant page and send to you. be tomorrow tho'.

Clive