电火花小孔内圆磨床
small hole electrical discharge internal grinding machine
椭圆内接三角形
inscribed triangle within the ellipse
圆内接多边形
inscribed polygon of a circle
圆内接外切系
poristic system of circles
圆内接正n边形
regular polygon inscribed in a circle
圆周钻孔圆头螺母
round nut with drilled holes in side