Bolt size is 5/16" X 24 pitch (fine threads) X 4", If using it more than once, change out the eye bolt to a one piece ring bolt. Apply anti-seize grease to the threads of the bolt before inserting them, this works great and if you purchase some all thread rod, you can use the puller for removing the rear bearing carrier from the lower unit when you need to replace the prop shaft seals or remove the gears.
Thanks to IrishBassin for the pix.