TABLE JACK FOOT DEVICE FIELD OF THE INVENTION The present invention relates to a device for levelling an item of furniture. BACKGROUND OF THE INVENTION In many instances, it is difficult to prevent a table from rocking as there are no adjustable feet. Adjustable table feet are known and typically comprise a threaded foot threadably received by the table leg. The present inventor has observed that such an arrangement is unsatisfactory as the exposed threaded stem on the top of the foot is damaged or bent by people kicking or placing their feet on it. Further, the adjusting knob of the adjustable foot is dislodged and lost leaving the threaded stem exposed, making it impossible to adjust. Apart from this, it also creates a hazardous situation. The disadvantages outlined above can often result in an unsteady table and spillage of drinks or the like. SUMMARY OF THE INVENTION According to a broad form of the invention, there is provided a device for use in adjusting the level of a piece of furniture having a support member with a bore extending through a bottom surface thereof and into the support member, the device having; a foot, a threaded stem having a first end attached to the foot and a second end, a tube having an upper end and a lower end, a flange projecting from the lower end of the tube, whereby the second end of the threaded stem is threadably received within the lower end of the tube, whereby in use the tube is slidably received within the bore such that the upper end of the housing is finger manipulable for rotation relative to the foot until the flange engages the bottom surface, such that rotation causes the tube, flange and bottom surface of the furniture support member to threadably travel towards or away from the foot so as adjust the level of the furniture. 1 The present invention also relates to a table or a support section having the device of the first broad from of the invention fitted thereto. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic cross sectional view of a preferred device of the present invention fitted to a horizontal fin that forms from a Thable base; Figure 2 is a schematic view of the device of Figure 1 in use with a table; Figure 2 is a further preferred device of the present invention fitted to an end of a table base leg; Figure 2a is a schematic view of the device of figure 2 in use and Figure 3 is a schematic view of yet a further preferred device of the present invention fitted to a leg of a stool or bench. DETAILED DESCRIPTION OF THE INVENTION The device is essentially made up of six components hereafter referred to as "parts" as follows: PART ONE: Is a bush machined from stainless steel or other durable material. It is 20.0mm in overall diameter for 3.0mm then steps down to 12.7mm outside diameter for 4.0mm making the overall length of the bush 7.0mm long. The bush also has a 3/8" internal thread to accept the threaded stem of the adjustable foot. PART TWO: Is a 12.7mm outside diameter stainless steel tube with a maximum wall thickness for adequate strength but must leave a bore diameter to afford clearance for a 3/8" threaded adjustable foot stem to move freely inside. This tube is then cut to a predetermined length which is governed by the thickness of the table base fin or base plate etc. Once cut the tube is then welded to the 12.7mm diameter end of "part one". The 20.0mm diameter end now provides a shoulder for an anti-ware washer to sit on. This washer is "part three". PART THREE: Is a 19.0mm outside diameter x 12.0mm inside diameter x 1.5mm thick nylon flat washer. PART FOUR: Is identical to "part three" a flat washer. This part slides over "part two" and is also used as an anti-ware washer as well as a cover. 1A PART FIVE: Is a 15.8mm outside diameter stainless steel tube with a wall thickness of 1.2mm giving it an internal diameter of 13.4mm. This diameter is just big enough to allow it to slide freely over "part two". "Part four" is cut to a minimum of 5.0mm long in the case of a base having the top and underside of the table fin running parallel. This tube will act as a spacer which will be discussed later. PART SIX: Is a stainless steel turning knob approximately 25.0mm in diameter and 15.0mm long. It can also be made in mild steel, brass or plastic with a variety of finishes. Part two is flared out slightly at the 12.7mm diameter end to allow a press fit for permanent fixing. The end of the adjustable foot stem is burred over by a burr punch to prevent the adjustable foot from coming out and being lost. 1 B The physical dimensions of the "device" can also be varied to suit its intended use or purpose. FITTING THE DEVICE TO A TABLE BASE: Once having identified the style or type of table base that the "device" is to be fitted to, and in this case a four star finned existing table base, all four existing adjustable feet are first removed. (Can also be 3 and 5 star) With the assistance of a drilling jig, a 13.0mm hole is drilled through the internal thread (which previously housed an adjustable foot) and continuing through the top of the fin, or visa versa which ever the operator prefers. Now slide "part three" over "part two" until it sits on the shoulder of "part one". Pass "part two" through the newly created 13.0mm diameter hole in the fin from the underside of the fin leaving the extra length of "part two" protruding. Slide "part four" over "part two" until it sits on top of the table fin. Next slide "part five" over "part two" until it sits on part four". There must be enough of "part two" protruding to allow the turning knob "part six" to be pressed onto "part two" and bottom out leaving just enough clearance in the complete assembly for turning without wobbling or rattling. Just prior to fitting the turning knob with the assistance of a burr punch, punch the top of the adjustable foot stem and burr the last thread over to prevent the adjustable foot from being screwed out completely and becoming lost while in use. The next step is to fit the selected adjustable foot by screwing the 3/8" thread into "part one" until it is in as far as it can go. A measurement is now taken from the bottom of the adjustable foot and the underside of the table fin. Add approximately 5.0mm to 10.0mm to that dimension and this is the position the other three adjustable feet must be locked in to. Now place the table in the upright position on a flat surface (floor) which should leave the adjustable foot fitted to the "device" approximately 5.0mm to 10.0mm up off the flat surface (floor). Press down on the turning knob "part six" so that the adjustable foot fitted to the "device" touches the floor. Turn the turning knob "part six" in an anti-clockwise direction until all four adjustable feet are firmly on the floor eliminating any table rock. Page 2 When the table is placed on any uneven surface or returned to a flat surface the turning knob "part six" is turned either anti-clockwise for up adjustment or clockwise for down adjustment until all four points are firmly on the floor in order to prevent the table from rocking. You will notice that the underside of the turning knob "part six" will always have the same gap between it and the top of the table fin no matter how far it has been adjusted. The adjustable foot does not turn. The "device" is effectively a jack. Because of the design, the thickness of the table fin or table base plate etc, has no bearing on its effectiveness as long as the combined length of "part one" and "part two" is 1.0mm longer than the length of the threaded stem of the adjustable foot fitted to the "device". In actual fact the "device" can be fitted to stools, bench seats and chair legs in the same way as stated earlier. All that is needed is for the length of "part two" to be increased to the desired length. The "device" and or any part thereof can be made from a range of different materials providing that such material offers sufficient strength and durability for its intended use. The materials should be selected as to avoid rust or corrosion caused by electrolyses due to direct contact of dissimilar metals in harsh or corrosive conditions. The physical dimensions of the "device" can also be varied to suit its intended use or purpose. It may be appreciated that the device is unique in its design because: (a) the turning knob stays at the same height in relation to the top of the fin or base plate to which it is attached. This prevents a person damaging the threaded stem by kicking it or placing their feet on it; (b) the turning knob is very close to the top surface of the table fin or base plate keeping ti well out of the way so as not to cause a person sitting at the table discomfort or injury by constantly kicking it or piercing their foot by an exposed thread rod after the knob has been unsecured and removed by vandals or just worked loose and fallen off; (c) it can be easily fitted to most centre column table bases no matter how thick the fins or base plate is as the device is not reliant on the length of the threaded stem of the adjustable foot for its successful use. In fact, the device will fit most standard adjustable feet in the market place making it very serviceable should the occasion arise that the adjustable foot need be replaced. 3 The device can cope with different thicknesses of table bases as it is a simple matter of varying the length of "part two" and in some cases "part five" also to suite the intended recipient table bases design during manufacture of the device or can be left longer than needed and simply trimmed down on site to suite the table. (d) the device can easily be fitted to existing table bases on site and in matter of minutes with very little or no disruption to a business or public place; (e) the device is a cost effective solution to the age old problem of rocking tables and is suitable for most types of floors; (f) the device can also be include as part of new table bases during manufacture or at the final assembly stage of same; (g) the device can also be used on four point tables, bench seats, stools and chairs, and is especially effective for levelling furniture pieces being used in outdoor situations, on sloping footpaths where you would fit a device to two legs, not only to stop the rock but to also level the piece of furniture. 4