Referring to the section shown in Fig. 35, the measuring screw _S_ is secured to the thimble _B_ with the screw _D_, the head of which is hardened and forms the anvil. By loosening this screw _D_, the thimble can be rotated to compensate for wear. The wear of the measuring screw and nut is taken up by screwing the bushing _A_ into the frame with the wrench shown in Fig. 37. This bushing is split in three sections for about two-thirds of its length on the threaded end. The three small lugs on the wrench fit into these slots. The handle end of the wrench is a screw driver which is used for manipulating the set screw _C_. The bushing is made an easy fit in the frame on its plain end and tapered, as shown, on its outside threaded part. This thread being the same pitch as the measuring screw, adjustment for wear does not affect the reading of the micrometer. This manner of adjustment brings the nut squarely down on the measuring screw for its whole length, presenting the same amount of wearing surface after adjustment as when new. [Illustration: Fig. 36. Handle for Inside Micrometer] [Illustration: Fig. 37. Wrench used with Inside Micrometer] The point _F_, which is hardened on its outer end, screws into the frame, and is secured by the taper-headed screw _O_, which screws into and expands the split and threaded end of the point _F_. The handle, Fig. 36, clamps over the knurled part of the frame for use in small, deep holes. The rods, six in number, running from 1 to 6 inches inclusive, are made by screwing a sleeve onto a rod with a hardened point and locking it with a taper-headed screw on its threaded and split end, the same as in the point _F_. The extension pieces, Fig. 38, are adjustable, on their socketed ends, in the same way, and run in lengths of 6, 12, 18 inches, etc.[19] [Illustration: Fig. 38. Adjustable Extension Pieces for Inside Micrometer] Direct Fractional-reading Micrometer [Illustration: Fig. 39. Direct Fractional-reading Micrometer]