A general term applied to a variety of flat-sided iron spikes, that are driven into the joints of brick-work, against which it is desired to fasten any kind of wood-work; for this purpose, the other ends of the holdfasts are spread out so as to lie flat against the wood, whereto these are nailed or screwed through holes made in the iron. The term holdfast is likewise applied to those iron ties in the form of the letter S", which are commonly fixed to walls to keep the mass from separating.