Responding to several replies at once, yes this is the "anti-rotation"
nut on a mechanical Tost brake. Whether there should be any "wonder"
about the bolt failing depends a lot on how hard I was pulling on the
brake. While I braked harder than I normally do, it was with a
pressure I felt comfortable with and I was surprised that the brake
would break under those circumstances. I know I have on occasion
pulled harder on the brake in other gliders. And the failure did
_not_ occur at the time of maximum pull, so I guess some details of
this particular incident are in order.

The landing was on a old WW2 base with wide and long runways. I
misjudged my approach and landed faster than usual and beyond the
runway start markers where I normally touch down. I normally turn off
at the first turnoff (760 feet beyond the runway start) but did not
know if I could do that this time. So I pulled as hard as I felt
comfortable doing to see what would happen, intending that if I could
not get stopped by the first taxiway I would go to next one 300 ft
further down. But I did get slowed down enough to take the first
taxiway. I actually released pressure on the brake as I went into the
turn because I wanted to be sure of having enough speed to get to the
runway incursion markers on the taxiway (the turn is more than 90
degrees). After the turn was completed I could see I had more than
sufficient speed and tried to again pull on the brake but found no
response. So I think the bolt sheared during or just after the turn.
I found myself looking at the spinning prop of a facing airplane on
the same taxiway, just beyond a crossing (runway-paralleling) taxiway,
and thought "I'm going to have to do something drastic if this thing
does not stop before I get to that crossing taxiway!" Thankfully I had
correctly judged the speed needed prior to the turn and with full
spoilers I did stop about 20 feet beyond the runway incursion markers,
just before reaching the cross taxiway.

So possibly the additional side forces during the turn did something.
Another possibility is that heating of the brake by the heavy braking
prior to that point helped cause the bolt to fail. It has been
suggested by a private email that the bolt tempering may have been
faulty. FWIW the brake was newly installed by an aircraft mechanic
(not me) but one who has limited experience with gliders. I will plan
on taking some pictures the next time I visit the plane. All I know
at this point is that there is a nut on that bolt at the brake case
(as a spacer?) and the shearing occurred just outside that nut. I
assume that the missing bolt part was attached to the plate extending
from the fuselage for that purpose. I had had about 10 successful
landings since brake installation, but all with minimal braking.

My reason for bringing this failure to this forum was because I was so
surprised by the bolt breakage given the amount of force I applied, a
force I did not feel was undue based on my past experience with Tost
brakes, so was looking for comments by those who might have
knowledge/experience that I do not. I would be more understanding
about a bolt breaking if I felt I had pulled extremely hard. I really
believe that the force I applied was not unreasonable.

I would like to think my braking capability is limited only
by pad friction, not by the strength of some bolt or other part of the
brake! Certainly for my car that is the case - my car's braking is
not limited by part of my brake assembly failing. I certainly hope my
ailerons/rudders are that way - I don't want to think that if I yank
too hard on the stick my ailerons/rudder might break off ! If there
is some amount of pull beyond which a brake part will break, one will
never know just where that point is until a pull actually does go
beyond that point and the brake then breaks - so one never knows
exactly how much stopping power one has until after he's broken the
brake once.

Jack