The Answer . . .

to your burning question is: 
A boar needs his clockwise corkscrew penis end to lock safely into the cervix of the sow. Her cervix is 3.9 to 9.7 inches long and has transverse folds that form a counterclockwise corkscrew pattern. Without a secure, lasting lock between the two at the height of the mating process insemination could not be guaranteed because of possible slippage during the lengthy ejaculation. The climax in pigs lasts about 30 minutes. So say the experts. (Swine Production Glossary; informedfarmers.com)

Now you know.