The Nails that are up on ebay are mid-90's reactive - NOT urethane. The original urethane Nail was the same hardness as the pink hammer, and an EXCELLENT dry lane/spare ball. The logos are different. Look them up on the other site (bowlingballreview.com) The Nail reactives up on Ebay are the equivalent of a C300 Beast - a mild reactive low flaring ball, good for medium-dry conditions, and just so-so as a spare ball for the average bowler because they will hook when they hit the dry.
The Blue Pearl, Black ,Red, and Blue urethane balls all have the same weight block. They will not flare more than 1 to 2 inches. The Blue Pearl urethane will hook the least, the Black urethane would be next, followed by the Red, and finally the Blue urethane hammer. If you want a spare ball, the Blue Pearl would be excellent. The Black works well too if polished. The Red might backend a bit too much for corner pins, but can work. The Blue urethane is an excellent hard hitting ball that works well on medium-light to medium-heavy oil conditions. The Black and Red urethane balls polish very easily - the Blue urethane does not polish well at all. If you don't mind playing straighter lines, the Black & Red urethane hammers are effective on oily conditions when dull/sanded. Lastly, being urethane balls, they do not like lanes with carrydown - especially with the oils used today. If I was to buy any of those balls listed, I would get the Blue Pearl as a spare/torched lane dual purpose ball, and maybe a Blue urethane for a "never gonna wear out" practice ball.
