Metric (sort of) fastener wierdness - does this make sense?

[Doug Shepard]

I decided I needed a handful of connector bolts and cross dowels for a project. No problem - they're all 1/4-20 and there are plenty of sources, sizes, and finishes. Then I notice that every other aspect of the fasteners except the connector threading is metric. The diameter of the bolt heads, allen socket size, cross dowel diameter, hole offset and length are all in metric. Here's a sample from LV's site but they're all this way as near as I can tell
http://www.leevalley.com/hardware/page.aspx?c=2&p=45375&cat=3,41306
Not a huge deal but it means I need to also pick up a couple of metric brad point drill bits. I need the bolt heads flush with the surface so I need to counterbore. LV doesn't carry a 17mm brad point or forstner that will fit th head so it's off to W.M Fuller. They hybridization is lost on me. seems like these would or should have a metric thread size too, or be comletely Imperial,. Anybody know if there's a logical reason behind this?

[Curt Harms]

but some Grizzly machines I've assembled had a mixture. SAE threads and metric hex heads.

[Rod Sheridan]

Hi Doug, I think the issue is that so few countries in the world aren't metric.

It is probably easiest to change the thread from 6mm to 1/4-20 UNC. and leave all the other aspects the same.

Of course, I don't understand why they wouldn't simply provide the entire assortment in metric, unless they expect them to be used with other 1/4-20 UNC hardware.

Regards, Rod.

[Jay Jolliffe]

My ex-wife had a Chevy Malibu. I went to change the shocks the front was metric & the back was SAE. Or visa-versa....Don't remember the year.

[Cliff Rohrabacher]

You can make your own flat end drills for counter boring.

Grind the point flat.
then carefully grind a relief on the flat lands so it cuts not too aggressively though. A one degree relief is plenty Two is ok.

Drill to the depth with a regular drill of the same size and follow with your custom counter boring bit.
it's easy and works great.


When I had a machine shop at my disposal I'd make 'em from drill bits and grind the end of the drill with a pilot bushing sized just slip into the standard bolt clearance drill size. That's only necessary when you haven't pre-drilled the C-bore. You'd drill the clearance holl and just shove that C-bore bit in and Viola. When you don't have a pilot bushing you just pre drill to the right depth or a little less.

[glenn bradley]

It the rest of the world making the concession to we holdouts since we buy so much stuff ;-) I was taught metric in the early 60's but we just never went ahead and converted. A great mistake for whatever the reason was. At least I speak both now ;-))