the invention will now be described in detail in relation to a preferred embodiment and implementation thereof which is exemplary in nature and descriptively specific as disclosed . as is customary , it will be understood that no limitation of the scope of the invention is thereby intended . the invention encompasses such alterations and further modifications in the illustrated assembly , and such further applications of the principles of the invention illustrated herein , as would normally occur to persons skilled in the art to which the invention relates . this detailed description of this invention is not meant to limit the invention , but is meant to provide a detailed disclosure of the a mode of practicing the invention . referencing then fig1 - 6 , shown is the instant tool comprising generally two subassemblies , namely a clamp subassembly 1 and a housing subassembly , or housing 16 . shown is the clamp subassembly 1 having a gas cylinder 2 disposed therein in a secured position . a gas cylinder 2 means any type of pressurized cylinder , strut , or piston used to provide resistance , for example with any device that opens and closes such as a door or table . shown herein as an example only is the use of the instant tool for the underside of a fold - and - roll table gas cylinder . such cylinders can range from 95 - 220 lbs of compression rating . therefore , the instant tool is adapted to compress a gas cylinder 2 and maintain the gas cylinder 2 in a fixed position while the entire implement with the gas cylinder 2 is located at the desired position such that the gas cylinder 2 can replace an already mounted , pre - existing cylinder efficiently and safely . clamp subassembly 1 is generally c - shaped to include an elongate arm 3 , an upper jaw 4 , and a lower jaw 5 . “ generally ” c - shaped means the upper jaw 4 and lower jaw 5 extend from the arm 3 as would be typical for a c - clamp device , but the arm 3 need not be linear nor do each jaw have to be linear and perpendicular to arm 3 , although preferred . a handle 6 can be disposed at any location along arm 3 or upper jaw 4 to aid in maneuvering the clamp subassembly 1 . the desired type of handle 6 as shown is a lock - tight type handle 6 which raises or lowers the upper jaw 4 and upon lowering “ locks ” the upper jaw 4 in its down - most position . upper jaw 4 extends from upper end 7 of arm 3 . a spindle 8 is configured to move vertically through upper jaw 4 and is disposed through upper jaw 4 as shown , the spindle lower end 9 of spindle 8 configured to engage one end of the gas cylinder 2 . for example , the spindle 8 is threadedly connected through a hole defined in upper end 7 such that upon manually rotation of the spindle 8 the spindle 8 travels up or down and thus “ axially ” in relation to arm 3 through the hole as would be understood . lower jaw 5 is disposed along arm 3 distal to upper jaw 4 , extending therefrom similarly to upper jaw 4 with its length of extension substantially similar to the length of upper jaw 4 so as to have its lower jaw 5 outer end 10 substantially aligned with spindle 8 of upper jaw 4 . lower jaw 4 may include an adjustment means for sliding lower jaw 5 up and down ( axially ) along arm 3 , thus being movably positioned along arm 3 to vary the length between spindle lower end 9 and the lower jaw outer end 10 in large increments . accordingly , gas cylinder 2 can be placed within and movably fixed between upper jaw 4 and lower jaw 5 as shown . the tower jaw 5 , described in more detail , includes a lower channel member 11 disposed at lower jaw outer end 10 . lower channel member 11 is mounted to lower jaw outer end 10 in one embodiment using a screw such that lower channel number 11 can be raised or lowered slightly in small increments . further shown is how lower channel member is sized to have accommodated therein one eye receptacle of the gas cylinder 2 . in the preferred embodiment the lower channel is u - shaped such that its extended portions can engage the eyelet in a cup - like fashion . however , it is not critical that lower u - channel be precisely “ u ” shaped as shown in the preferred embodiment . however , it is critical that it not be flat , thus of a shape which provides for any means to forcibly abut the eye receptacle while enveloping the eyelet in some manner , such as a curved plate or cup - like member , which additionally may be case - hardened in any fashion . the upper jaw 4 , described in more detail , includes a similar upper channel member 13 disposed at spindle lower end 9 . spindle 8 is formed as an elongate bolt or any type of threaded , cylindrical pin adapted to travel through upper jaw outer end 10 . upper channel member therefore travels with spindle lower end 10 . in a preferred embodiment both the upper and lower channel members 11 , 13 are attached to their respective locations loosely or with a free spin attachment so that bolt can be tightened or loosened for fine adjustments or moved to match the angle of each cylinder eyelet rather than move the eyelet 2 a itself to align with a static u - channel . in either embodiment , shown is how upper channel member 13 is sized ( similarly to lower channel member 11 ) to have accommodated therein the opposing eye receptacle or eyelet 2 a of the gas cylinder 2 to thereby confine the gas cylinder 2 . as with the lower channel member 11 , it is not critical that upper channel member 13 be precisely u - shaped as shown in the preferred embodiment . however , it is critical that it not be flat , thus of a shape which provides for any means to forcibly abut the eyelet 2 a while enveloping the eyelet 2 a in some manner , such as a curved plate or cup - like member , which additionally may be case - hardened in any fashion . fig6 shows an embodiment wherein a leveraging extension bar 19 can be utilized with the handle 6 for increasing leverage . now referencing fig5 , shown next to clamp subassembly 1 is housing 16 . housing 16 is a means for immobilizing the cylinder 2 as it is clamped by clamp subassembly 1 . defined on housing 16 is housing channel 17 , for instance two raised , generally parallel guides 18 a , 18 b up - stand from a base , i . e . along a length of the housing 16 . the gas cylinder 2 is placed within the housing channel 17 . the guides 18 a , 18 b therefore maintain the cylinder 2 in a relatively stationary position . in this manner , the clamp subassembly 1 can be more easily and accurately secured to each eye receptacle or eyelet 2 a of the cylinder 2 , which expectedly could roll around and move about a flat surface if merely placed thereon . in use and with particular reference to fig4 , described herein is a method for replacing a gas cylinder 2 at an underside of a table 14 , summarized by the steps of : measuring a length of an installed gas cylinder ; removing the installed gas cylinder ; setting a clamp 1 on a new gas cylinder 2 , wherein the clamp 1 is set to approximately the length of the installed gas cylinder obtained from the step of measuring ; moving the clamp 1 with the new gas cylinder 2 engaged thereto to the underside of the table 14 ; while still engaged to the clamp 1 , bolting the new gas cylinder 2 to the underside of the table 14 ; and , releasing the clamp 1 from the new gas cylinder 2 , as a result leaving the new gas cylinder 2 at the underside of the table 14 . more particularly , the fold - and - roll table 14 is positioned such that the underside is slightly upright or otherwise made accessible , revealing the old , in - place cylinder , i . e . the “ installed ” gas cylinder . the length of the installed cylinder is measured in - situ , in its compressed position , for example the length between the bolted - in eyelet 2 a receptacles which are mounted to the table &# 39 ; s mounting holes . the old cylinder is removed . the clamp subassembly 1 with its handle 6 in a downward position is set with its u - channels ( channel members 11 , 13 ) spanning a distance which approximates the measurement . the clamp &# 39 ; s handle 6 is then released to unlock the clamp 1 . the new cylinder 2 to replace the old cylinder is placed on a flat surface , preferably within housing 16 . the clamp subassembly 1 with its handle 6 in an up position is placed over the new cylinder 2 and engages the new cylinder 2 by way of the handle 6 of the clamp 1 being pushed downward to “ lock ” the cylinder 2 between the u - channels 11 , 13 . the handle 6 of clamp 1 pushing down therefore forcibly compresses the cylinder 2 to the same measurement as previously noted for the old cylinder . the clamp 1 with the compressed cylinder 2 therein is then taken to the installation location and still while within the clamp the eyelets 2 a of the new cylinder 2 are aligned with the same mounting holes of the table &# 39 ; s underside . the length of the new cylinder 2 can be finely adjusted using the adjustment bolts if need be . the cylinder 2 is then fastened using bolts through the eyelets 2 a , and the clamp 1 is released , leaving the newly mounted , replacement cylinder 2 , replaced without having to jostle and maneuver the entire table 14 , without requiring two individuals , and without having to compress or maneuver the new cylinder 2 at the confined and potentially dangerous mounting location underneath the table 14 .