What is the most difficult single pin for the right handed bowler to pick up for a spare?

A 4-6-7-9-10 or 4-6-7-8-10 split, according to a Slate Magazine analysis of thousands of pro Bowling shots, is the hardest spare to pick up. The toughest spare you're likely to actually get stuck with is the 7-10...you pick this up by hitting one of the pins so hard it bounces off the sideboard or the backboard and flies into the other pin.