the small rod is just a carriage bolt ... 5/16" I needed to make it smaller because if I up the size to 3/8" then the 5/8" rod gets too weak. for me it was either deal with super cheap carriage bolts or risk breaking a rod. a new bolt can be purchased from depot or lowes for pennies. since I haven't bent a 5/16" rod yet ... it might be you got a soft one or applying a little too much pressure. don't need much more than maybe 10 ft lb torque to seat the crank. or were you referring to something else bending?