Box I Double I C Plain rectangular Routed A 6A recommended 5A minimum 2A 6A recommended 5A minimum 15A minimum No fittings within these limits Direction of grain if spruce or outer  face grain if  plywood 1 /4 A A Figure 6-21.  Typical splice repair of solid rectangular spar.  Figure 6-22.  Typical splice repair of solid rectangular spar. Local damage to the top or bottom edge of a solid spar may  be repaired by removing the damaged portion and fabricating  a replacement filler block of the same material as the spar.  Full width doublers are fabricated as shown and then all three  pieces are glued and clamped to the spar. Nails or screws  There are numerous tools made by individuals, and there are  commercial plans for sale with instructions for building scarf-  cutting tools. Most of them work, but some are better than  others. The most important requirement for the tool is that it  produces a smooth, repeatable cut at the appropriate angle. 6-17