美国采购需求：狗狗训练项圈、无线狗狗围栏、防吠项圈、GPS追踪器、狗狗驱赶器、止吠项圈

I'm looking for collars for my two small pups, a miniature schnauzer and a toy poodle, both 6 months old. They have very petite necks, so it's crucial that I find collars that fit without any adjustment. Could you please let me know the smallest size available? It's important that these collars can't be adjusted any smaller, as that would not work for my dogs. I appreciate your help!