wringbolt

from The Century Dictionary.

• noun In wood ship-building, a large ring-bolt or eye-bolt used in conjunction with a wring-staff to force the outside planking into position in building a vessel. Also called wrain-bolt.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Shipbuilding) A bolt used by shipwrights, to bend and secure the planks against the timbers till they are fastened by bolts, spikes, or treenails; -- not to be confounded with ringbolt.