Lugs not staying tight

Are there washers? The bottom of the nuts have a shoulder that goes in the wheel, the clearance is fairly tight.

As far as torque the sbp stud is 7/16"-20 thread, standard wheel torque is 55 to 65 ft-lbs. The special lug likely has more friction on washer and sides, so 70 to 80 ft-lbs is typically used on Cragar wheels. I have used 70 ft-lbs without a problem for the past 20 years.