The 5/16 is used for the majority of our holds. Use this size for Socket Head Bolts. The 7/32 is used for the 25 Assorted Smalls. Use this size for Flat Head Bolts. The T bar is larger and easier to handle than the L Bar. If you are building a large wall, it is recommended that you purchase a T Bar; otherwise the L Bar will do the job just fine.