Just had a discussion with a shearing customer about the benefits of 9 tooth and 9 tooth cover combs. Here are the options for types of combs. To my understanding.
Let's see. 7 tooth "blowout", 9 tooth cover, straight 9, 13, 17 mohair, 20, and 24. Those are basically the options for number of teeth on a comb.
7s are phasing out. Some people out west still use them, but they're being replaced by 9s. They're dangerous. I don't dare even try using one. Think about it, the width of the comb is the same...but it has fewer teeth, so the gap between each tooth is greater. You even need a "wyoming special" handpiece, and 3 point cutters rather than 4 to run a 7. No thanks.
9 tooth combs are common. They're easier to push through the wool than a 13, and leave a little more wool, protecting the sheep from sunburn and cold. the cover 9s have raised bumps on every other tooth to, in theory, leave even more wool. In my opinion, they're just harder to use. 9s are good if you're used to them, especially in dirty or dense wool, because the pushing isn't as bad. For example, when I sheared out west on nasty Ramboillets. 9 tooth combs were the only comb for the job.
13s are your standard comb. My favorite. pretty much all I use around here. If they still made 12s, I might prefer a 12, but I've never found anything better than 13. User friendly, easy to use, do a nice job, and leave enough cover to protect the sheep.
17 is made especially for shearing angora (mohair) goats. Eh just throw on the 13.
20 and 24 are for really smooth bellys on show sheep. Don't think I'd want to shear an entire sheep with one.
That's today's lesson, kiddies. Go buy a packet of 13 tooth combs.