New and improved design! Semiautomatic build kit for the STEN Mk5. This closed bolt system works extremely well and eliminates the problems of kits offered by other companies. You will need this kit, one of our tubes (), and an original MK5 parts kit in order to build a legal semi automatic firearm. This kit includes the following high quality American made parts: a semi-auto bolt, cocking handle, standard AR-15 firing pin, roll pin, firing pin spring, bolt stop, guide rods, rod retainer, 2 sets of springs, and assembly instructions. Two small parts need to be welded together. Please note that the bolt uses a STEN Mk2 or Mk3 style extractor. Design is based on our ATF approved Mk3 model. Other US made parts may be needed to be compliant with GCA 18 U.S.C. 922r.