NR prop bolt concern

[Delta Whisky]

Brian - it would take a very experienced structural engineer with plenty of metallurgical experience to give a full and complete answer to your question on this subject. John touched on two of the high level answers so I'm just saying what he did in an different way.
1. you can more often trust the properties of AN, MS, NAS, etc. spec'd bolts sourced from respected aircraft hardware businesses than more common bolts sourced from places that serve other industries. (And, yes, we have experienced forgeries/counterfeit in the aviation world but those events are much more likely to be detected earlier than "grade" bolt variation.) and,
2. their ductility is felt to be beneficial in that it might offer a chance for detection of an overloaded condition in a properly designed application. (The designer will often want the bolt to yield - not break - rather than one of the fastened parts breaking.) It is really a case of "strong enough" with other performance benefits being included by the designer.

I too run a NR prop and really like its performance. I was surprised to see the bolts that came with it though. Not knowing much about 8.8 bolts, I used them and haven't (yet?) had a problem but that is what the designer spec'd so I went with them.

[avidflyer]

Delta Whisky, Have you ever taken any bolts off to get a look on the hub of the prop to see if you are having the same issues as I did? JImChuk

[Delta Whisky]

Delta Whisky, Have you ever taken any bolts off to get a look on the hub of the prop to see if you are having the same issues as I did? JImChuk

Jim - good question. This forum subject got me to thinking that I should. Because the plane is down for an equipment swap and because I've wanted to change the pitch for cold weather, your question is the final motivation I needed. If I can get it all in before the rain comes in tomorrow; tomorrow will be the day. Darrel

[Delta Whisky]

Delta Whisky, Have you ever taken any bolts off to get a look on the hub of the prop to see if you are having the same issues as I did? JImChuk

Jim - a short vacation and a bout with Covid kept me from getting to this until today. To me, all look normal. There's about 280 hours on these bolts since last loosened for a prop adjustment.
Propeller bolts at 280 hours.jpg

Darrel

[Av8r3400]

So why do we use the equivalent to grade 5 bolts on something that is obviously very critical, high stress, high-vibration (possibly)?

Yield strength and ductility are more desirable than hardness in this application.