What's the reason for boxend set size spacing?

[nelstomlinson]

I have three sets of double boxend wrenches. The way the sizes are distributed across the wrenches is a bit different on each set, and it doesn't quite make sense on any of them.

I have a set of SK stubbies that are laid out 6x7, 8x9, 9x10, 11x12, 13x14, 15x16, 17x19,18x20mm.
I have a set of craftsman raised panel boxends that go 6x8, 7x9, 10x11, 12x14, 13x15, 16x18, 17x19.
I have a set of Snap On high performance zero degree boxends that go 6x7, 8x9, 8x10, 10x11, 12x13, 12x14, 14x15, 15x16, 17x19, 18x20, 21x22, 22x24.

I was expecting a pattern like even and odd, even and odd (like 6x7, 8x9); or even and even, odd and odd (like 6x8, 7x9), but each of these three sets does a bit of both. They have overlaps in sizes I wouldn't have thought were common, like 9mm in the SK set and 14mm in the Snap On, but the SK and craftsman don't have two 12mm ends!

I am noticing a similar lack of pattern in my SAE wrenches. Is there any rhyme or reason to this? Do these combinations of sizes cleverly maximize the utility of the wrench sets, or do are they just random?

 

[Dallus]

Maybe if you're using a wrench of one size, there's a good possibility you'll encounter a bolt with the size of the other end of the wrench. I know on some nissans without auto tensioners my SO 12/14 is great. I just loosen the pulley with the 14, flip it around and use the 12 to remove the tension. Maybe I'm the only one who's done that.

 

[nelstomlinson]

Maybe if you're using a wrench of one size, there's a good possibility you'll encounter a bolt with the size of the other end of the wrench.

Dallus, that sounds like a vote for ``cleverly maximizing the utility.''

I keep thinking there must be some story behind it, like ``You need two nines for the Citroen Deux Chevaux brake adjuster, and you need to use the 17 and 18 together to refrobinicate the 1956 Mercedes E450 framistat, so the 17 and 18 can't be on the same handle, and ...''

 

[ajchien]

I am happy to have a 14x15 box end wrench. The 14 fits the serpentine belt tensioner bolt on my Honda, and the 15 fits a 1/2 drive breaker bar on the other side to give me more leverage. Instant replacement for a serpentine belt tool.

 

[MattT]

Some "odd" metric double box size pairs make sense when you figure in the different head size standards which vary by country. For example a guy who only wrenched on japanese cars would only want 8x10, 12x14 and 17x19 wrenches.

Not sure if they still do it but Snap-on used to carry several different size pairs so folks could buy the wrenches sizes suited to what they were working on.

 

[expatriated]

It would be awesome if someone made custom designed box ends. You pick the two ends you want. So, I could order a 10x19, something crazy like that. It would save space in a motorcycle tool roll for me anyway.

I'm sure it would be too cost prohibitive but it would be cool.