The countertop is 24" deep, Formica on 3/4" particle board. The supplied retaining clips are long enough to grasp the bottom of a 3/4" counter, so they are okay for the sides. At the back, there is one extra support making the thickness there 1.5". At the front, from top to bottom the thickness is 2.25". Here's how it looks: https://www.flickr.com/photos/90278919@N00/16216641888/
Top photo is looking toward front; bottom, looking toward backsplash.
Had to call Kohler to order extra long screws. They had the 2.5" size that I needed. (Even longer ones are available.) I think there are 12 to a package for $10.00, plus $14.95 for expedited shipping (2 - 3 days). The gal gave me a break, charging $5.00 for the clips, making the total $19.95. Still, I'm without a sink probably to Monday.
What really pisses me off is that Kohler supplied with the sink clips that only work on 3/4" counter. Certainly my house isn't the only one on the planet with extra support at the front over the double-doors, and at the back. I would cost them virtually nothing extra to supply 2.5" with every SS dropin sink. The extra lengths on the sides wouldn't cause any problems. Shame on greedy Kohler.
Here's what they look like at the 1.5" length. Note the outrageous price.
http://www.lowes.com/pd_639063-28557-LK363_0__?productIdP271229&Ntt=sink+retaining+clips&pl=1¤tURL=%3FNtt%3Dsink%2Bretaining%2Bclips&facetInfo Just venting here.