What size allen wrench do i need to tighten the door handle on model 6 bar, which is a smaller wine cooler? is it metric or standard?

There are nuts or allen bolts for both the stem and the bars. They are almost certainly a metric size, but hard to say what unless one has the same bike. My guess would be a 12mm hex, plus or minus, or a 6mm allen, again plus or minus. Get a metric hex/allen set and see what fits.

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Allen wrenches are sold in sets and not expensive. Moens are not metric so any set of small SAE allen wrenches will contain the right size for your Moen.

Go to the hardware store and purchase smaller wrenches. They could be either metric or SAE.

There is a long vertical handle held to the door by two short horizontal pieces. Run your finder along the under side of the two short pieces and feel for a very small indentation under each one. Each one is a set screw with an Allen head. Insert a small Allen wrench (English not Metric -- I don't know the size, but it is probably the next to the smallest in the set) into each one and back them out (counterclockwise looking up at the screw). The big vertical handle should come off when you back the Allen screws out far enough Now look into the short pieces sticking out from the door. Inside each one is a Philips screw holding the piece to the door. Tighten those screws with a small Philips screw driver making sure that the indents on the front of pieces will align with the vertical bar when you put it back on. When the Philips screws are tight, put the vertical bar back on and tighten the Allen screws. If you have some Loc-Tite, you might use that as well.

It is a 1/8 inch allen wrench. Do not overtighten the bolts. You can crack the wood. Wishing you a happy baby!

Not sure about the size but it might be an imperial allen wrench or maybe a metric size.
Just a thought.

6 mm to small 8 mm to big, how about 7 mm would you not think ??

Just did this on mine today. Use an allen wrench to back off both the upper and lower set screws (Note: you do not need to back them all the way out). The handle will then easily pull away from the door. With a 1/4" socket, tighten the screws holding the upper and lower lugs on the door. Place the handle back on and tighten the upper and lower set screws.