seriesinner diameter of the eyehole(mm)inner diameter of the back surfaceabout the eye hole's number and position k2481256,near the center of the circlek3481276,near the circumference of the circle.more pictures: a: b: c: more about the products: material:45#steel means:casting bottom:quadrate, with 4 holes in the surface some flange yokes of series 140 and 153's eyeholes have a low position. 1,we are professional manufacturer with 30 years experience 2,we haveadvanced processing and testing equipment to guarantee the qualityof products 3,we provide various kinds of products according to customers'requests 4,high quality and low price;heat-resisting and no distortion 5,good serve