Abstract: To further expand the product range of the seamless steel tube, and increase both the cost-effectiveness and the profit, the 261 mm groove of the Mini-MPM is designed and developed by a domestic seamless steel tube plant. Mandrels as used for rolling operation with the said groove are all recovered mandrels as properly-processed. The minimum pipe wall thickness as rolled with the groove is 6 mm. Relevant actual operation practice shows that with the newly-developed groove, it is possible to perform on-line continuous rolling operation to produce steel pipes with wall thickness accuracy and both inner and outer quality meeting the contractual requirements.