I attempted to change my cleat (to the new hard indestructible type) but broke off a cleat bolt. The cleat nut on the inside of my Shimano carbon shoes is a triangular nut that joins all three cleat bolts. On I tried to drill out the bolt with no joy. Shimano don't sell triangular nuts anymore (only sort of plate things, with part number ESMSHRP900CLNT) so I cut the busted apex of the V off.
I then used a
claw nut (or T nut) as the third cleat nut.
The problems were
1) The cylinder of the nut was too long. I had to grind it down once before insertion and again to remove the portion of the cylinder protruding from the bottom of the sole.
2) The little claws on the claw nut were not going to register (make holes in) the rock hard carbon sole. Fortunately my penultimate nut left marks where the claws had tried and failed to get into the carbon and I drilled four 2mm holes from those marks. I made the holes bigger, 2.5mm, from the outside and eventually managed to get the three of the four claws to register. It is important to bash the nut into the sole with a hammer and steel rod, till the T of the nut is firmly up against the inside of the sole, rather than to attempt to turn it in using a nut from the outside, because the little claws will bend as you turn unless they are fully embedded with the T plate of the nut up against a surface.
Here is what it looked like from the outside.
New Cleat Nut by
Timothy Takemoto, on Flickr
Here it is with a new slippery hard plastic cleat. I may grind the apexes of the cleat a bit to give it more friction. Their hardness is wonderful but at first they are like skates.
New Cleat by
Timothy Takemoto, on Flickr
EDIT
1) I could drill from the outside. Durr.
2) I could make a simple die, perhaps out of an aluminium plate, with a large bolt protruding in the centre to centre the die, and four holes properly placed for the little claw nut holes and drill through them.
Then I could easily replace all three cleat nuts on each shoe quite quickly. I have ordered more M5 cleat claw nuts from here
https://www.aliexpress.com/item/32898135040.html