the space between the bottom of the base section 16 and the bottom of mid section 17 to the sprockets 54 shown in fig2 the chains 60 are trained on the sprockets 54 and pass therearound and thence forwardly to an anchor 63 fastened to the bottom of the fly section 18 just forwardly of the anchor 63 is an anchor 64 similarly connected to the bottom of fly section 18 and connected to the anchor 64 are a pair of chains 65 which extend forwardly from the anchor 64 around sprockets 58 and are connected by an anchor 66 to the bottom of base section 16 when the cylinder 40 is actuated it will cause the mid section 17 to extend and retract relative to the base section 16 and when the midsection 17 extends the sprocket 58 will move away from base section 16 and will exert a pull on chain 65 causing it to pull out the fly section 18 reverse movement will cause the sprocket 54 to move and to pull on the chain 60 which will retract the fly section 18 the above construction and operation are generally similar to that disclosed in john l grove u s pat no 3 809 249 issued may 7 1974 referring now to fig3 there may be seen the base section 16 mid section 17 and housing 35 together with the connections between housing 35 and mid section 17 and between.