For rivets in tension with counter-sunk heads, the tensile value shall be A. Reduced by 25% B. Reduced by 33.3% C. Increased by 25% D. Increased by 33.3%

The correct answer is: A. Reduced by 25%.

The tensile value of a rivet is the maximum amount of tensile force that the rivet can withstand before it fails. For rivets with counter-sunk heads, the tensile value is reduced by 25% because the counter-sunk head creates a stress concentration at the top of the rivet. This stress concentration can cause the rivet to fail at a lower tensile force than a rivet with a flush head.

Option B is incorrect because the tensile value is not reduced by 33.3%. Option C is incorrect because the tensile value is not increased by 25%. Option D is incorrect because the tensile value is not increased by 33.3%.