When I’ve been abroad I have seen the snails sold in tins and the two varieties of snails most commonly found on menus and in their stores are the escargots de Bourgogne and the petit gris. The petit gris are about one third the size of the escargots de Bourgogne. I have also occasionally seen the achatine variety in markets. This is a tropical variety from Africa and Asia that can grow to half a kilo in size, but is sold in France at the same size as the escargots de Bourgogne, which are normally described as gros (large) or extra gros (extra large).
As I mentioned, snails are commonly sold canned. Small cans, 200 grams gross weight, will contain either 4 dozen small, 3 dozen medium, or 2 dozen large snails. The next size up is three times larger and contains a proportionate number of snails. Canned snails are cooked in a court-bouillion prior to canning and some of the cooking liquid is packed along with the snails. The cooking liquid may be as simple as water, salt, and spices, or it may also contain some vegetable matter. Before use, the snails should be thoroughly drained and then rinsed under flowing water. The canning liquid is either discarded or reserved, depending on the recipe. If the recipe calls for small snails and all you have is large ones, the snails can be cut in half without affecting the finished recipe.