TM 10-1670-298-20&P Table 2-3.  Stitching Specifications Component Recommended Sewing Machine (Code Symbol) Stitches Per Inch Thread Size A-21 Cargo Bag' Cover MD 7 to 11 E Strap Keeper DN or ZZ Darn E Sling Scuff Pad MD 7 to 11 E DN or ZZ Darn E V-Ring Hole Reinforcement MD 7 to 11 E Main Strap Keeper HD 5 to 8 3 Sling Strap and Loop HD 5 to 8 5 Quick-Release Strap HD 5 to 8 5 Safety Clip Retaining Strap MD 7 to 11 E Strap with Ring HD 5 to 8 5 A-22 Cargo Bag Cover HD 5 to 8 3 Cover Lacing Loop Strap HD 5 to 8 5 Sling Assembly Scuff Pad HD 5 to 8 3 DN or ZZ Darn E Scuff Pad Edge Reinforcement HD 5 to 8 3 Support Web LHD or HD 5 to 8 5 Lateral Strap LHD or HD 5 to 8 5 Tie-down Strap LHD or HD 5 to 8 5 Suspension Web VHD 5 to 8 6 f. Darning and Zigzag Sewing Repairs. (1)   Darning. Darning  is  a  sewing  procedure  used  to  repair  limited  size  holes,  rips,  and  tears  in  assorted airdrop  items  constructed  from  textile  material  such  as  parachute  canopy  gore  sections  and  the  cloth  and reinforcement webbing of deployment bags, packs, and cargo.  A darning repair may be made either by hand or  sewing  machine,  depending  upon  the  method  preferred  and  the  availability  of  equipment.    However,  a darning machine should be used to darn small holes and tears where fabric in missing.  Darning of previously patched  material  can  be  performed  provided  darning  size  limitations  prescribed  In  the  applicable  item equipment publication are not exceeded.  A darning repair will be performed using the following procedures, as appropriate: (a)   Machine Darning. 1 Using an authorized marking aid of contrasting color, mark a square around the damaged area and insure  that  the  marking  is  at  least  ¼-inch  (0.635  cm)  back  from  each  edge  of  the  damaged  area. The marking will be made with the warp and filling of the material 2 Darn the damaged area by sewing the material in a back and forth manner, allowing the stitching to run with the warp or filling of the fabric (A, Figure 2-1). 2-12