在现场对测量三翼刮刀钻头、三牙轮钻头及三棱扶正器等由三个均布圆弧或点所决定的圆的外径,以往都是用铁环固定式的钻头规,因为它的尺寸是单一的,不可改变,使用起来很不方便,既费时又麻烦且不准确。后来出现了一种可调的圆环式的钻头规,这比过去的单一尺寸的铁环固定式钻头规要好得多,它可以方便地测量一个范围内的各个尺寸,而且所测的数值也比较准确, In the field on the measurement of three-blade scraper bit, tricone bits and three centralizer, etc. by the three uniform circular arc or point of the circle determined by the diameter, the past are used iron ring fixed drill rules, because it The size is single, unchangeable and inconvenient to use, both time-consuming and cumbersome and inaccurate. Later, an adjustable toroidal bit pattern appeared, much better than the conventional single-size ferrule fixed bit pattern, allowing easy measurement of individual dimensions over a range and the measured values More accurate,