a the hinge spring 121 attached to the housing 1 and the jaw 105 partially shown hidden lines is oriented with the first and second ends 124 125 in the same plane biasing the jaw 105 to the open outwardly extending position as a result of the orientation of the spring 121 relative to the stationary hinge spring holder 122 further showing the spring action in greater detail in fig1 b when the jaw 105 hidden lines is urged to a more compressed position the stationary holder 122 retains the spring 39 s first end 124 orientation however the rotating spring holder 123 allows the spring 39 s second end 125 to be rotated with the jaw 105 rotation of the spring 39 s second end 125 as the jaw 105 is compressed twists the spring 121 into torsion as soon as the force causing the jaw 105 to pivot to the compressed position is released the spring 121 biases the jaw 105 to return the jaw 105 to the casing engaging position once again further the preferred construction of the hinge 107 avoids supporting loads imposed on the jaw 105 when in the casing engaging position the jaw 39 s conduit 120 and the bore 143 of the rotational spring holder are both oversized relative to their respective retaining pins 133 145 allowing limited lateral movement of the jaw 105 relative to the housing i without interfering with the jaw 39 s pivoting action accordingly when the jaw is in the outwardly extended casing engaging position the reaction on the jaw 105 drives the jaw sufficiently into the housing 1 so that the.