can be used to hold the material transfer unit 501 inside the shield 145 once the shield 145 and material transfer unit are ready to proceed into the mine the pin can be removed fig1 b shows an exploded cross sectional end view of the piggy back truss conveyor type of material transfer unit 501 showing greater detail of the components including the truss side frame 430 which is a structure to support the conveyor independent of the shield 145 the top belt rollers 433 to support the conveyor belt 437 carrying the material the bottom belt rollers 435 to support the return belt 439 roller guides 447 to keep the belt 437 amp 439 in alignment wheel rollers 443 are supported by heavy duty springs 445 to help support the roof 405 as the material transfer unit 501 is pulled out from within the shield 145 in the event of a roof fall and subsequent extraction the units 501 are preferably hooked together by placing a hook 453 over a pin 441 fig1 c shows a cross sectional side view of the unit 501 with head pulley 450 and tail pulley 451 shown the unit 501 is shown clearly situated within the shield 145 such that the shield 145 provides protection against rocks falling from the roof 414 of the mine and provides a cavity for withdrawing the unit 501 from the mine in the event of a roof cave in fig1 d and 1 e show.