TM 9-243 FACTORSTO CONSIDER WHEN USING GAGE BLOCKS - Continued Error  range Error  range millionths   of millionths   of C/ass Work an  inch Class Work an  inch I Verifying  gages,  setting 5 to 20 III Setup of grinding, milling 40 to 100 instruments, and tool and drill machines, and inspection. parts  inspection. I I Layout of jigs, fixtures and 20 to 40 dies,  setting  instruments, and tool inspection. CARE  OF  RING  AND  SNAPGAGES 2 Always consider the abrasive action of the part on the gage. Cast iron, steel, and cast aluminum are more abrasive than brass, bronze, and nonmetals such as plastics. Use particular care when gaging cast iron, steel, and cast aluminum. 3 When gages are stored, arrange them neatly in a drawer or case so that they do not contact other tools or each other. 4 Always hold the gages in your hands when check- 1 Always make certain that the surfaces of the parts ing. Never clamp them in a vise. gaged and the gage itself are kept free from abra- 5 At frequent intervals, check all gages for accuracy sives, dirt, grit, chips, and all foreign matter. and wear with gage blocks or master gages. CARE OF GAGE BLOCKS 1. Observe  particular  care  when  using  gage  blocks  to measure  hardened  work.  The  danger  of  scratching is  increased  when  the  work  is  as  hard  as  the  block, or harder. 2. Never touch the measuring surfaces of blocks any more than necessary. The moisture from your hands contains an acid which, if not removed, will eventually. stain the blocks. 3. Before  using  blocks,  ensure  there  is  no  grease,  oil, dirt, or any foreign substances on block. 4. Every time a set of blocks is used, all the blocks which  have  been  cleaned  for  use  must  be  covered with a film of acid-free oil, such as boiled petrolatum, before they are put away. Wipe them with an oiled chamois as you return the blocks to their places in the case. 15-9/(15-10    blank)