Driftless Climbing Bolts for Indoor Rock Climbing Holds. These are 3/8-16 thread socket cap screws that will fit standard climbing hold t-nuts. The bolts come in packages of 25 and you may choose between 1.5 inch length for small holds and feet. 2 inch length for small to medium holds 2.5 inch length for medium to large holds. 3 inch length for large holds. (The 2.5" and 3.0" have 1.5" of thread.) These are high quality industrial steel bolts that will minimize misthreading and stripped threads. These bolts are for indoor use only and come with a thin coating of machine oil to minimize rust and corrosion, but these bolts should not be used on outdoor walls as they will rust over time.