The higher the blade number the shorter the trim. For a pre-surgical shave you would use a 40. A 7F should leave about 1/8 inch of hair. That seems rather short for a winter clip unless you are planning on having Henry wear a sweater all winter. A 5F would leave around 1/4 inch, a 4F would leave around 3/8 inch, and a 3F would leave around 1/2 inch. I tend to keep my poodles at around 3/8 to 1/2 inch on their legs and 1 to 2 inches on their bodies in the dead of winter.
We used to get our Cocker Spaniel trimmed short every winter because he always got spectacular ice balls on his legs. One autumn we missed his shave down, so he went into snow season with proper thick Cocker Spaniel feathering. No ice balls. His long feathers insulated his legs so well that his body heat didn't melt the snow, and the outer layer of hair stayed dry enough that it never collected ice. Alas, my poodles don't have the same snow repellant hair as the Cocker Spaniel did, so leaving their hair long just means bigger ice balls stuck to their legs.
We used to get our Cocker Spaniel trimmed short every winter because he always got spectacular ice balls on his legs. One autumn we missed his shave down, so he went into snow season with proper thick Cocker Spaniel feathering. No ice balls. His long feathers insulated his legs so well that his body heat didn't melt the snow, and the outer layer of hair stayed dry enough that it never collected ice. Alas, my poodles don't have the same snow repellant hair as the Cocker Spaniel did, so leaving their hair long just means bigger ice balls stuck to their legs.
