BTA is an external cooling and internal chip removing type of deep hole drilling. The drill head and drill stem is connected by screw. The rigidity is higher than gun drill and the drilling efficiency is 2-4 times higher than gun drilling. BTA deep hole drilling requires higher oil pressure and sealing between workpiece and guide sleeve. This type of deep hole drilling is suitable for constant and heavy volume drilling because of high efficiency. Limited by inner space of drill stem, BTA drilling is mainly used in drilling diameter Φ16 – 65mm of deep hole, http://www.gsmdrilling.com