Abstract: The danger of a jib falling off a boom due to an erroneous operation during movement of the jib between a stowage position and an extended position is eliminated. The jib is provided with a pivot pin insertion state detector, pivot pin retraction blocking element, a coupling pin insertion state detector, first and second cables, wherein movement of a coupling pin to a retracted position is restricted by a coupling pin retraction blocking element via the first cable when the pivot pin insertion state detector has detected that the pivot pin is retracted, and movement of the pivot pin to the retracted is restricted by the pivot pin retraction blocking element via the second cable when the coupling pin insertion state detector has detected that the coupling pin is retracted, so that simultaneous removal of both of the pivot pin and the coupling pin is prevented.

Abstract: The danger of the jib falling-off due to an erroneous operation both during an operation to extend the jib from a stowage position to an extended position and during an operation to stow the jib from the extended position to the stowage position is eliminated.

Abstract: A method for sealing a zinc-aluminum pseudo alloy spray coating, which comprises forming a zinc-aluminum pseudo alloy spray coating on a substrate to be spray-coated, and then sealing the surface of the coating with a chromium-free sealing material containing phosphoric acid in an amount of from 0.1 to 7 wt %.

Abstract: A jet printing ink composition comprises 2 to 60 wt.% of a binder precursor of an alkoxysilane having the formula R.sub.4-n Si(OH).sub.n (n=0 to 2; and R represents a C.sub.1 -C.sub.4 alkoxy group, methoxyethoxy, ethoxyethoxy or phenoxy group) or an oligomer thereof; and 25 to 95 wt.% of a solvent for said alkoxysilane or oligomer thereof; 0.001 to 5 wt.% of a solvent soluble acid; and 0.1 to 8 wt.% of a solvent soluble dyestuff, if necessary, further comprises up to 2 wt.% of a solvent soluble inert silicone oil for inhibiting blotting and up to 3 wt.% of an electroconductive agent.