into the reciprocal female straight threads 11 of a compressed gas cylinder 10 an u201c o u201d ring typically made of rubber and a backup ring typically made of a synthetic fluorine containing resin such as teflon neither shown create a seal between the bullplug 300 and the cylinder 10 the bullplug 300 includes a bore 302 which is in fluid communication with the contents of the cylinder 10 a valve 103 and a shear protection device 101 attach to form a valve and shear protection device 100 which attaches onto the downstream side of bullplug 300 allowing the operator to manually control gas or liquid flow from the cylinder 10 in one disclosed embodiment the bullplug 300 includes female straight threads 304 on the downstream side that screw directly onto reciprocal male straight threads 130 of the valve and shear protection device 100 however a variety of various attachment techniques are available without detracting from the spirit of the invention as is shown in fig2 a 2 b 2 c 2 d 2 e 2 f 2 g and 2 h the valve and shear protection device 100 is formed from a valve 103 and a shear protection device 101 the shear protection device 101 includes a shear tube 109 a poppet 112 a seat plug 118 and a retainer plug 124 the valve 103.