This allows the preforming of Marquise, Oval and Shield shapes. Fitting onto the outside diameter of the Spindle, it provides up to 30mm of offset, calibrated in increments of 0.1mm. Four keyed dops are included. Instructions include tables for standard stone sizes, and a method for calculation of offset for any combination you’d like–You should understand that preforming is not a absolute necessity–after preforming, you are still going to put the dop into the Spindle and proceed with faceting, and you might want to do that in the first place. But, if you like the controlled feel of having a preform before faceting, the Offset Attachment is for you. It is easiest to use along with a Dial Indicator Attachment.