Why Do Imperial Sockets Sometimes Fit Better On A Metric Vehicle?

[ReganAndCarter]

I'm re-starting some overdue repairs on my van that I had to delay. Today, when removing the two upper strut mounting bolts from up inside the wheelarch, the 16mm socket seemed a bit sloppy on the bolt head. If I rounded these off it would be a total 'mare due to access and them being quite tight. As I have done in the past, I tried some imperial sockets and found the 5/8" fitted a lot better. A perfect fit.

The bolt heads weren't worn or rounded, so why does it often turn out that imperial sometimes fits better than metric on a vehicle that definitely would be completely metric? Just curious.

 

[Stivino]

Your 16mm spanner or nut might be a bit worn and 5/8" is slightly less than 16mm.

 

[just pumps]

Sometimes it is the quality of the tools.

 

[Burnerman]

I find with older vehicles, the layer of rust has a deceptive sizing on nuts and bolt heads.....I’d suggest that a 15mm socket tapped on would be correct.
No need though, if the imperial socket fits well that’s just fine.
I would recommend full hexagon sockets though if you possibly can.
John

 

[Mottie]

I have a socket set especially for those nuts on the top of shock struts that have a couple of flats on the thread to put a small spanner in to stop it turning. Full hex sockets. Paid well over a hundred quid for it probably 15-20 years ago. I think I’ve used it twice!

 

[ReganAndCarter]

Thanks for all your replies. Just Pumps might be close as I checked the 16mm socket and it's from a budget socket set bought some years ago. Though the 16 seemed ok when used on other bolts. Maybe if my collection of Draper Expert sockets contained a 16 it might have a better chance of fitting. Not the first time I've found a metric to be sloppy and tried an AF instead for a better fit.

Thanks to Mottie for a shot of those tools. Not looking like they've done a lot of work.

 

[mointainwalker]

Thanks to Mottie for a shot of those tools. Not looking like they've done a lot of work.

Which must be making him pretty sick

 

[ReganAndCarter]

While we're on the subject of nuts, bolts and fixings, I have one more question. When I was underneath on my back I noticed the subframe was attached with some strange bolts that I've never seen before. Only way I can describe them is the bolt head wasn't a normal hex, it looked like a torx driver bit. What are these called?

 

[Stivino]

External Torx head bolts?

 

[ReganAndCarter]

External Torx head bolts?

Thanks, knew it would be something simple like that. Suppose they give better grip and are less likely than hex bolts to be rounded. Or poss just easier to use on a production line.

 

[Stivino]

I Googled it.
The Torx drive eliminates all the disadvantages of the classic Phillips drive. Like the hexagonal drive, it is also available as an inner and outer profile. The Torx drive offers a much better grip than most other drives, there is no axial force or cam-out effect, slipping off is almost impossible.

Advantages:

• The Torx drive offers much better force transmission than most drive types and its parallel profile flanks prevent axial forces from pushing the bit out of the fastener head when tightening.
• Because the force is transmitted over a larger surface and centrally, this drive system involves extremely low wear and can also be used by assembly robots.
• The absence of a cam-out effect protects the fastener head and very high torques can be applied.
• The tightening action can be effected quickly and safely.

 

[Burnerman]

Very common on French brakes (ATE) and BMW bikes they are called Star drive.
Evenly numbered from E6 to E18 size, but I have needed E20 before.
John

 

[fixitflav]

I'm re-starting some overdue repairs on my van that I had to delay. Today, when removing the two upper strut mounting bolts from up inside the wheelarch, the 16mm socket seemed a bit sloppy on the bolt head. If I rounded these off it would be a total 'mare due to access and them being quite tight. As I have done in the past, I tried some imperial sockets and found the 5/8" fitted a lot better. A perfect fit.

The bolt heads weren't worn or rounded, so why does it often turn out that imperial sometimes fits better than metric on a vehicle that definitely would be completely metric? Just curious.

Perhaps the bolts are 7/16" UNF or UNC, in which case 5/8" AF would be correct. 16mm AF is not the right size for any metric bolt - M8 - 13mm, M10 - 17mm, M12 - 19mm. Though on vehicles they sometimes use non-standard head sizes for some reason.

 

[Avocet]

5/8" is 15.875 mm so therefore just a wee bit tighter than 16mm on the bolt head. I absolutely second Burnerman's recommendation to use 6 sided sockets. 30 years ago, I started seeing "flank drive" or "face drive" sockets, which had rounded lobes on each of the 6 faces. The idea was that they would drive against the flats of the bolt head, rather than on the corners. I thought they were brilliant, but I don't see them much these days.

 

[Harry Bloomfield]

30 years ago, I started seeing "flank drive" or "face drive" sockets, which had rounded lobes on each of the 6 faces. The idea was that they would drive against the flats of the bolt head, rather than on the corners. I thought they were brilliant, but I don't see them much these days.

I bought myself a full set, around ten years ago, thinking what a clever idea. They slip onto rusted heads much easier, seem much more tolerant of head wear, as well as driving much better than the 12 sided sockets.