KathyJ,
The best way to ensure this is to contact directly KA and ask about the model you are buying, they have a lot of customer feedback on the plastic gears issue.
I checked a KA brochure I got at Macy's last month. It indicates mixers KL26M8X (Pro Line), KP26M1X (Pro 600 series) and KV25GOX (Pro 5 series) are the only ones with all Steel Gears Direct-Drive Transmission. All other mixers are listed at having "Direct-Drive Transmission" which I deduct uses plastic gears.
Good luck with your search.
Please let me reflect on the subject on the direct drive transmission, if I may.
There IS a difference between plastic gears and nylon gears.
1. Plastic gears are what you might find in childrens' toys or the cheap flimsy
no-name hand-held mixers. This type of gear has low quality, is not very strong and can break even if a moderate load factor is placed on them.
2. Nylon gear transmissions are used in the lower-priced K'Aid Sand Mixers.
This type of gear- even though it might not be as strong and durable as metal, it is much stronger than ordinary plastic gears. They HAVE to be in order for the machine to plow through heavy doughs and batters.
I once sent an e-mail to K'Aid, asking if the K-5SS and K-45SS have metal gears in their transmissions. They wrote me back, saying that those two stand mixers have NYLON gears for their transmissions.
They also said that it's to help protect the motor, for if an abnormal amount of strain is ever placed on the mixer, the gears would strip, but the motor won't wimp out, saving the cost of a new motor over getting the gears replaced.
But in order for the nylon tranny to wimp out, you have to be doing something awfully bad for that to happen. In normal use, the tranny will give many, many, many years of reliable service.
So don't let the "plastic" transmission fool you. It can take it. And K'Aid Stand Mixers, reguardless of the model number, is made to handle bread and cookie dough as well as heavy cake batters.
But the Onyx Black Artisan mixer now has metal gears.