Canadian (CISC) Bolt Holes are Looser than American (AISC) Holes?

[chris457]

I'm curious on the history of this. AISC says all holes shall be 1/16" larger than the bolt size (recently increased to 1/8" for larger bolts, but 3/4" and 7/8" are still 1/16" larger for 'standard' holes). CISC says all bolt holes shall be 2mm larger (1/16" ~ 1.5mm). So they rounded up. Sure. BUT they also specifically make an exception to allow 3/4" to use 7/8" holes and 7/8" bolts to use 1" holes, since imperial bolts are often used... I guess they just rounded up again instead of going back to the AISC standard 1/16" larger. Nothing has fallen down in Canada due to this as far as I'm aware...but I sure did get a lot of questions from the detailer on an American project about 'oversized holes' when I specified 1/8" larger holes. I wonder if the AISC specification will get loosened in the future again for smaller bolt sizes. It sure seems like it would make the erectors life easier.

 

[CANPRO]

Where are you getting this information? Refer to CSA S16-19 Table 5. You’ll see +1/16” for 7/8” bolts and smaller, and +1/8” for 1” and larger.

 

[Enable]

I don't have my book with me today but my recollection is aligned with CANPRO. The difference between 2mm, as S16 treats it, and 1.6mm as treated in AISC is pretty moot in practice since many shops use imperial setups anyways. When I was a GC and we had large steel projects my steel subs would always RFI for a change to imperial - everything including the hole sizes, etc. Now that I am a steel sub of sorts myself I also use imperial gear.