Ron, I sell the wobblers and the offset one is to enable the operator to mount a DTI and offset it to allow a reading to be taken around the outside of a shaft to centralise it under the quill. I must admit though the I do not advise the use opf the item as I do not believe that they part is stable enough to hold an expensive DTI. I use alternative methods to hold the DTI. I hope the above helps. John MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.