Heat Treated Rake Teeth. Bluebird P18, PR18 and PR22 seeder models. 1/2 mount hole on one end. 52 blades per set. The only way to insure that you are ordering the correct part is to match this number to your application. This information is usually in your owner’s manual and sometimes stamped on the part you are replacing. You cannot rely solely on the fact that your model number may be listed in the description. The same model many times uses different parts per model year or serial number break. If you need help, send us the complete make, model number, and serial number. We are here to help.