My 80 tooth blade will ping a 50mm branch off without much bother .
Take a picture of the output shaft showing the shape or splines with any bits that fit under the strimmer head then I'll have a look at mine and see if I can identify anything for you, oh! you must have cow horns for saw blade...
Define wood cutting blade, I use a generic 80 tooth saw blade on mine as well as 2,3,4 and 8 tooth blades
Edit, when you say square shaft do you mean the one inside the main tube or the one that protrudes from the gear head
You would have to try and temper a nail to see if it can be hardened or anything made from forging them wouldn't hold an edge unless combined with a bit of alchemy
If I need probe a bit more rigid I shove it down a length of pex tube with the camera level with the end and if thats down a drain pipe I bore holes either side of a tennis ball and shove the pex through it so it keeps the lens up out of the wet
Soak your strimmer cord in water overnight to make it more supple and move the strimmer gradually closer towards the poles then move away before the cord start to wrap around
A fall arrestor could just leave you dangling ,not being able to go up or down .
I use a climbing rope going up over the roof anchored at ground level either side with some slack . I am then attached to the main rope with another short length and prusik knot, that way, if you fall you have the...
Cutting around the door would keep your visible board width even until very top ones. Directly above the door the board would be a little thinner where is cut around it so may need something under and over the door frame to shed water but you will be in a better position to see if needed ...
Its pretty neat software, when you run a scan of all the control modules it give a history of fault codes and milage when they were triggered.I don't think my aging brain will ever get to grips with all the weird and wonderful stuff I can do.