Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: What size drilled rubber stopper do you use with these to ferment food?  goes between the airlock and the recap lid
Document: I love this product. What a smart design. It works great too. Already made sauerkraut using this with an airlock & rubber stopper. I would highly recommend this product.
I have been using the regular mouth recap lids for over a year now and have been *extremely* happy with those. They never leak. I wish I could say the same for the wide mouth version.The frustrating thing is that they don't always leak. I will put some water and lemonade powder in the jar, screw on the recap lid (making sure the rubber seal is in place), and start shaking.
We get raw milk and transfer it to 1/2 gallon Mason jars. The reCAP makes it so much easier to use. GREAT PRODUCT!!! !
Since I have already invested the money in the lids, I will replace my seals. They are also working with the airlocks now and making a tight seal. I will continue to use them to ferment veggies. I am very happy with them now.
These caps are a great addition to canning jars, eliminating the mess when pouring liquids. I plan to use them for sun tea and also for fermenting foods with an airlock inserted in the spout. Very study design that will last a long time.
I love this lids!! they are easy to use and make pouring my homemade creamer SO easy. No more getting to much for my coffee. Also makes pouring fresh ranch dressing so easy. I can't say enough great things about the reCAP lids.
These are a must have if you like to use mason jars! There's a rubber seal so there are no leaks and the cap &#34;snaps&#34; so you know its closed! Great for shakes, dressings, sauces, drinks. I have even used it to dispense laundry detergent while traveling! I need to order more - so many uses for them!
I use mason jars for everything and I have the smaller version of these wide-mouth caps, too. The little rubber ring inside does not always stay in place. They can fall out and are easy to lose. Also, the price is sky-high. Can't wait for someone to start making cheaper ones, haha. The grippy part of the cap is too smooth to get a good grip, so they are hard to remove from the jar.
These leak on me sometimes. I wonder if my seals may be old, even  though I haven't had for very long. I bought them to also use for fermenting with the airlock and have a hard time getting them to be airtight, which I also attribute to the seal. I will buy new seals and try them again. If they worked as they are suppose to, I would love them!10/26/13 update: I did purchase 3 new seals and find that the lids are working properly.
I love these jar caps. I got them so I could put a plug and airlock on the hole for fermenting, but I have been using them for all sorts of things now.
Answer: Hello, I called my local brew shop and he measured the stoppers.  He recommends ordering a #5