Allen Keys, metric vs Inches

[adrian44]

A question: Do both variants come in identical sizes but only the marking on them is different, or there are sizes in one type that aren't made in the other?

 

[cotjocky]

Not sure if I understand what you are saying. But SAE is SAE and Metric is Metric. Two totally different systems of measurements. Some sizes are close to one another and can be used as a substitute. Example 3/4 and 19mm are really close to the same size, but they are not exactly the same.

 

[adrian44]

"Not exactly the same" is the answer I was looking for. Thanks.

 

[Socophreak]

Not the same, but will be close. For stuck screws/bolts make sure you have the right one as you can strip either the tool or the bolt head.

 

[nelstomlinson]

Generally, it's ``close enough to trick you into rounding the fastener,'' not ``close enough to do the job.''

 

[darkzero]

For hex keys, IMO opinion sizes can't substitued. For sockets & wrenches I rarely even use standard, I use metric for most standard sizes (but not all). But for hex keys the sizes between metric & standard are not close enough to prevent damage to the hex socket head or the hex key. For tightening or loosening under torque I won't even try.