On 25/02/2021 20:02, newshound wrote:
On 25/02/2021 18:51, Fredxx wrote:
On 25/02/2021 18:28, Tim+ wrote:

I happened to stumble upon an old Hayter electric start lawnmower
chucked
into the long grass by a road whilst out for a jog the other day so Ive
brought it home to see if its repairable or has any bits worth
salvaging.

I started stripping it down and all the bolts were regular metric sizes
until I came to remove the engine cooling cowling. 10mm socket too
big, 9mm
too small.

It did occur to me that they might not be the original bolts so I
tried all
the AF and Whitworth spanners that I have. No joy.

Eventually dug out a cheap 9mm open ender spanner that could be
forced on
with a bit of percussive persuasion.

Im now inclined to think that they are original as they all match
and my
micrometer measures them up at 9.5mm.Â* WTF is the point of that?? How
many
socket sets include a 9.5?

My 3/8" socket would be at least 9.525mm, likely larger for a little
clearance. If this was a 3/8" bolt I would be surprised you squeezed a
9mm socket onto it, unless it was a 12 sided socket?

I cant believe that a designer decided that 9 mm would be too weak and
that a 10mm would be too cramped for space.

Briggs and Stratton has a US heritage so could well be imperial sizes.

Is the right answer. Could even be BSF/BSW. Although Hayter is British
(I used to work with a member of the family).

It is UNF or UNC. UNC is coarse for cast iron. UNF is the more normal.
9.5mm is a shade under 3/8"

a 3/8" AF should have fitted it like a glove. Almost certainly a 1/4"
bolt diameter.

--
"In our post-modern world, climate science is not powerful because it is
true: it is true because it is powerful."

Lucas Bergkamp