Witch S/S fitting to weld ?

I'm doing keg conversions and I need to know witch S/S fitting will work best.
I'm buying fittings from Stainless Steel Fittings they have two kinds.
1. half in threaded MPT half coupling O.D. machined 304S/S @ $1.68ea
2. half in threaded NPT half coupling O.D. machined 316S/S @ $2.25ea
I don't weld so I'm hireing a pro and want to bring him the best stuff.

which fittings? well i assume you mean NPT for both as that's what they have listed on the web site...MPT is another thread designation too...just something to be aware of.

304 and 316 are different grades of stainless steel (the 316 has more corrosion resistance)and they have different properties..but for brewing i would just use the 304 stainless.

I really just wanted to know witch S/S 316 or 304 welds better to a keg. or if they weld the same. Like I said I have no experiance with welding.

You might want a full coupling so you can connect a drain tube on the inside.

Type 316 holds up to corrosive environments better than 304, but this is not an issue for a keggle. Type 304 is fine and is usually cheaper, so that is what you should get. Your keg itself is type 304 SS. I have a mix of 316 and 304 fittings in my kegs, and there is no discernible difference between them.

MPT is a designation for Male Pipe Thread. FPT means Female Pipe Thread. Both are NPT (National Pipe Thread) unless otherwise stated. So the two items you have listed differ in gender as well as metal type.

Normally you weld 1/2 inch full female couplings into the keg. Full couplings are preferred by most people over half couplings for the drain valve so you can attach a pickup tube on the inside. For thermometer or thermowell and sight tube fittings, a half coupling is fine. I used only full couplings in my kegs anyway.

This is what I recommend for all of your couplings: 1/2" Threaded NPT Coupling OD Machined 304 SS R=1.54 S=1.08

Both 304 & 316 can be welded.
What you really want is 304L or 316L. The L versions are specifically formulated for welding and will produce more reliable welds.
You can hear a well informed podcast dealing with that topic here: The Brewing Network.com - Brew Strong: Brew Strong: 09-29-08 Metals that Affect Your Beer

As a welder in the Navy for many years, I can tell you, it doesn't matter. My welds on the one will be just as strong and pretty on one as on the other. You can use the same filler rod for both. S.

buy which ever you wish and take it to a shop with a tig, and them them do their thing if you have never welded before