On a solid wall (ie 9in brick), can crack stitching bars be fitted from the inside.

Usually there are outside only, so does it make any difference to fit from inside?

no expert but would have thought it needs to be done on both at that thickness
this off course would only be visible on the outside but as i say i don't have a clue

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we are all ------------------still learning

I've seen it done, but you'll have to remove plaster etc and make good if done on the inside?
The companies that make them like helifix or twist fix have helplines you can use

They are normally fitted to the outside skin, but if yours is a solid wall, nothing wrong with fitting them inside.