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Unused bolt hole for safety wiring

I would assume that since the engine is from Austria that it is a metric bolt. More than that I cannot say. I would, however, add that on two occasions I helped a couple of guys with RV-8s trying to find a wrench fitting the nut for the alternator wire. These alternators are from Japan. Ergo they use a 10mm socket.
 
I can tell you the threaded bosses in the gear box are M8, so compare the size of the one to which you’re referring to those. Hard to tell from the photo if it’s the same size.
 
In the photo below there is an unused bolt hole below the oil filter that I want use for a safety wire location for the magnetic plug. It seems to accommodate a 3/8 inch bolt, but I have no 3/8 inch bolt that matches the threads of the hole. Can someone tell me the bolt size and threads per inch to use here.
https://jimmccarter7132.smugmug.com/My-First-Gallery/n-qMcDSh/i-5sL4wGx

It is most likely M10 x 1.5, if it is around 3/8" diameter. I am not 100% certain for that particular bolt hole but others on the engine case are that size.

The 'normal' location for tieing the safety wire for the magnetic plug is around the existing socket head bolt that is in the crankcase above the plug. Just tie it around the head.

Also noticed in the photo that the safety wire for the oil pressure regulator plug appears to be going up, I don't know if it will be effective at that angle, on mine it is tied somewhere under near the oil pump to provide more security against the plug rotating out.
 
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You can drill a hole into one of the allen head bolts above or below it, not very difficult.
 

Seagull,
I don’t know a lot about safety wiring, but I’m skeptical that just looping the wire around the head of a bolt is an acceptable safety wiring technique. No matter how tight you make it, it seems there would be some chance it could slip off the head with vibration and expansion due to heat. I think drilling a hole through the bolt head is a good idea.
Answering the comment made by one of the other guys - my photo shows a safety wire going up from the oil pressure (I think) plug. I had safety wired this plug to the magnetic plug just as a trial to see if I thought it would work. However, I would rather use one of those unused bolt holes if I can find the right size bolt. I think it may be an M10-1.5 bolt as mentioned by one of the other guys. The hole does appear to have fairly course threads.
 
JimMac,
There is no chance the safety wire can climb the bolt head, the linear distance increases as the wire climbs the head.
 
JimMac,
There is no chance the safety wire can climb the bolt head, the linear distance increases as the wire climbs the head.

This is accepted practice for safety wiring the magnetic plug. Wire looped around angled socket head bolt cannot work loose when twisted wire is tensioned correctly.

I have 700TT and no problem...
 
You might want to use stainless steel socket head. The mild steel black-oxide bolt in your photo will rust in humid south.
 
Safetying

Also, if you're new to safetying, I most humbly recommend reading AC 43.13-1B "Section 7. Safetying".

Separately, Paul Dye wrote an excellent article in Kitplanes magazine on adding safety tie points, sorry I don't recall exactly which issue it appeared in.
 
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