For future reference 97-03,
Stock Front - 28mm - Hollow
Stock Rear - 17mm - Hollow
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GMPP Front - 34mm Hollow
GMPP Rear - 19mm Solid
Progress Front - 34mm Solid
Dorman Front - 34mm Solid
SLP Front* - 34mm Solid (35?)
SLP Rear* - 19mm Solid (25?)
BMR/Addco/Speedbuilt/Next Level Front - 32mm - Solid
BMR/Addco/Speedbuilt/Next Level Rear - 22mm - Solid
RAT Front - 38mm - Solid
RAT Rear - 27mm - Solid
Availability of most of these is limited. RAT are no longer made.
Apparently some users reported different sizes for SLP's. I got mine from craigslist so I'm unsure if they're legit SLP's or someone combined a different set.
SLP's on sale from 3800 report 1 3/8" thick for the Front and 5/8" thick for the Rear Sway Bar.