Fig. 1781.
Fig. 1782.
[Fig. 1781] represents Backus’ brace for driving bits, augers, &c., the construction of the chuck being shown in [Fig. 1782]. The two tongues are held at their inner ends by springs and are coned at their outer ends, there being a corresponding cone in the threaded sleeve, so that screwing up this sleeve firmly grips the tool shank and thus holds it true, independent of the squared end which fits into the inner tongue that drives it.
Fig. 1783.
