Metric drills and taps?

8.8 is a safe bet which is roughly equivalent to SAE Grade 5. For basic fastening SAE Grade 2 is most common with Grade 5 coming next which translates to metric 5.6 and 8.8 (Roughly...).

Anything below 8.8 in metric is often not marked.

To get a perspective, Grade 8 bolts are usually for stuff like automotive flywheels and torque converters with hundreds of horsepower behind it. You'll find Grade 5 for the bolts in small hydraulic press assemblies. Grade 2 is the typical zinc plated stuff found at the hardware store.


Ray




Analias said:
Ah, I may not have been clear. Perhaps I'm using the wrong nomenclature. I was curious what grade (quality/strength) you were purchasing your metric nuts, bolts, and screws at. The Wikipedia page for hardware (http://en.wikipedia.org/wiki/Screw#Machine_screws under the "Metric" header) says that metric goes from 4.6 to 12.9. Metric 12.9 ~= SAE grade 8.
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@Dubbie - Thanks. I really appreciate the input.

@Ray C - Excellent, just what I was looking for. So SAE grade 5 (metric 5.6 / 8.8) would be fine for mills and lathes.

Both of you have helped considerably to educate this newb. I'm sure I'm not the only who has had these questions. Thanks.
 
Grade 5 is closer to 8.8 rather than 5.6 but for what you're doing, sure... 5.6 or 8.8 will work.


Analias said:
@Dubbie - Thanks. I really appreciate the input.

@Ray C - Excellent, just what I was looking for. So SAE grade 5 (metric 5.6 / 8.8) would be fine for mills and lathes.

Both of you have helped considerably to educate this newb. I'm sure I'm not the only who has had these questions. Thanks.
Click to expand...
 
If you're not going to do a lot of metric drilling and tapping, buy the correct metric tap drill bit and tap for just what you need. Use the closest larger SAE bit for clearance holes. I like McMaster-Carr for one-offs: http://www.mcmaster.com/# If I (Minneapolis) order by 4pm I'll have it by 10AM the next day at ground rates.

Ken
 
I cannot buy the tapping sizes anywhere close to me so I ordered some online from down south (Sydney)
3.3mm and 4.2mm, no name on them just loose.
I have never seen twist drills so fragile before. Just looking at them they shatter they are so brittle.
Yes, one broke in a hole before it got anywhere close to break through (pillar drill) I'm always very careful there just in case.
Good job I had just finished the spark eroder.
Anyone have a source for good quality bits in australia in fractional metric sizes?
 
Give Sutton a call and ask them. They are an Aussie maker of quality drill bits. They should know the closest distributor.
 
For all practical purposes, to stock a few Metric fasteners, you should stick with 8.8 and 10.9 grades (SAE grades 5 and 8, respectively) 12.9 is a stronger grade than 10.9 or SAE grade 8, and is not commonly seen. The real confusion starts when selecting the thread pitch. Metric threads are specified by the distance from one point on the pitch line of the thread, and the same point on the very next thread. It is generally safe to assume that that distance is the same as the crest to crest distance, and that is easier to measure, but that's not what the specs read due to possible error in flank angle, etc. Metric threads some in several pitches for each diameter. Some people view this as a disadvantage, but it really isn't much different from SAE. We just use generalized terms like coarse, fine, extra fine, etc. The metric system is merely more specific. What might be considered equal to our normal "coarse" pitch might be (just an approximate example) a 5/16-18 would be an M8-1.25. A finer pitch would be 5/26-24, or roughly equal to M8-1.0. (Ray, 8mm is much closer to 5/16 than 3/8. 3/8 is close to 10mm.) In actual fact, there are fewer variations in the standard thread pitch specifications in the Metric system than the SAE system. Add to that we can have non-standard threads that are perfectly accepted by manufacturers. Just make it up, any machine shop will cut a 3"-24 if you want it, and a nut to match, and it is just considered a "special" and nothing is thought about it. I don't believe I've ever seen a Metric comparable thread situation.

So, when you get to order the assortment, stay with the standard "coarse" threads in Metric and you'll be fine filling 99% of your needs.
 
My pleasure, Analias. Part of my career was spent working two jobs, one of which was in Industrial Fasteners as a day job, and machine shop as a night job. I did this for 4 years, so learned quite a bit about nuts and bolts. Worked a few positions in that industry, from warehouse to inside and outside sales, and purchasing. It was a good experience, but the two job part was a killer. Helped pay off a house sooner though.
 
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