In the bush depression nest coat with a thin layer of red lead, under the three steel pad thereon grinding coloring the colored marks be repaired using a fine rasp or scraper blade, after three steel pad contacts simultaneously qualified, and then make the pad on the lower part steel pad thickness reduce 0.05 ~ 0.07mm, it can achieve scraping requirements. Note that identify colored marks, smear red lead oil too much is likely to cause the illusion.