everyone who fishes wacky rigs have seen the tool for it using rubber O-rings that slip over the worm....... well my question is what is the size O-ring they use?

I order 100 packs from ebay, they come in large or small.  The large is meant to fit the 6-7in baits but I usually use them for the 5" as well.  The small is meant for the 4-5".  As far as size I'm not exactly sure, I just go small and large.

Try Polyolefin Heat Shrinking Tubing cut into 1/8 or 1/4 inch strips and then shrunk onto your Senkos or finesse worms.

Will last for a very long time; protect your plastics; and are nto that expensive.

You will need an ignitor to heat the strips onto your plastics.

Just another suggestion to balance the O-Ring query. 

The correct O ring size is 3/8" OD  (Outside diameter) x 1/4" ID (Inside diameter)

The correct O ring size is 3/8" OD (Outside diameter) x 1/4" ID (Inside diameter)

Those would be the correct size.

You may want to try out heat shrink though.  It's far more effective than the o-rings.

3/8" electrical heat shrink tubing, no heat needed for the 5" Senkos.

3/8" electrical heat shrink tubing, no heat needed for the 5" Senkos.

^^^^

Yes