Fig. 11 represents a collar bolt or flange bolt. Such bolts are much used in engine-making, large and small. The quickest method of forging small bolts of this character is by drawing down or reducing the two stems from a rod or bar which is rather larger in diameter than the collar required. In the Figure the two stems are indicated by A and B. The reducing by fullers and ordinary hammers is a quicker process for small and short work than the method of making separate collars and afterwards welding them to their places. Collar bolts of great length are made by welding on separate collars, to avoid the lengthy process of reducing a piece of iron of large diameter. In a collar bolt, the strain upon the bolt while in use affects the collar in a small degree only; the principal strain is that of the nut below at the moment the bolt is fixed to its place, after which the working strain upon the upper stem of the bolt removes the strain exerted upon the collar by the nut below. Consequently, if the flange is not thoroughly welded, no great harm will result from that circumstance. But in all cases that require a clean, solid appearance to the bolts after the lathe process, great care in welding is necessary to promote the desired result.

If the smith who makes them receives proper instructions, he will observe that a screw is to be formed at each end of the bolt, and he will be careful to weld each end to ensure the necessary solidity in the screw. After the collar is welded, a square is needed to ascertain whether the sides of the collar are at right angles to the two stems, or whether too thick or irregular in one or more places ; if so, a set-hammer is used to rectify the irregularities; and if the collar is too thick, a trimming or paring chisel is preferable to cut off the ragged projections while hot; much time is thereby saved from the lathe process. The larger the bolt, the greater is the importance of the collar being at right angles and of suitable dimensions previous to the bolt being turned and screwed by a lathe.

Instead of bolts with circular flanges, bolts with four-sided flanges are sometimes used. The methods of making these consist either in drawing down the stems from a square bar, or in welding a collar to a circular bolt in the ordinary manner, and squaring the collar while at a welding heat by applying large angular gap-tools.