Yes, I made a big error. I was looking at Machinery's Handbook and quickly found the line "Alloy steel socket cap screws conform to ASTM574M property class 12.9....." I missed the line that said "Steel (hardware) conforms to SAE1199 or ASTM F568." A quick look at what is actually available for purchase would have made it obvious. Even so, Mcmaster Carr lists only two grades of M5 socket head cap screws, 12.9 and "unrated" stainless steel.

Pe, if you look just under the title of the bolt calculator you have a selection for metric, but material doesn't follow the metric grading system.

I took a few minutes to look up full scale practice. First, they don't seem to make many composite one piece props. Wood props are either tightened to a torque value or crush dimension (.006 inch per inch of hub thickness per Sensenich). Torque values specified for the bolts are stand torque values for AN hardware. But, standard torques for AN hardware is ~30% of ultimate stress. AN6 torqued to 200InLb as recommended by a [link=http://photos.imageevent.com/qdf_files/enginefiles/Installing%20Wood%20Propellers.rtf.pdf]Sensenich document[/link]. However, we all know that much time and effort was spent in engineering the proper clamping force and are often only certified for one type of engine.

Pe, the MVVS 50 shows 6 M5 screws on your technical drawing on your page. By torquing to a suggested 5.8 Nm (51 in-lb) for grade 8.8 in the chart you posted, this is 1300 Lbs of force PER SCREW! Pleas excuse the mixture of units. Times 6 bolts is 7800 Lbs! Do we really needs this much clamping force? A DLE 55 has 4 M5 screws, 5200Lbs. What does the prop manufacturer have to say? I would guess a single 3/8" nut would be 5000Lbs maximum.

I'd like to know how proper proper torque value is determined, not start any arguments or otherwise. Sorry that I have to ask why, but I never stopped doing that. I'm waiting for my 2 year old daughter to start.

Greg