A lightweight knuckle weighing substantially less than an AAR Standard Knuckle, is described for use in a railroad car coupler. This lightweight knuckle can be used, for example, to replace AAR Standard knuckle which becomes broken or otherwise damaged during operation and requires replacement in the field. Both the contouring and inner coring of an AAR Standard knuckle are radically changed to produce this lightweight knuckle which has all the functioning features of the standard knuckle, so as not to adversely effect the coupling and uncoupling operations of a coupler in which the lightweight knuckle is used.