Ryobi string trimmers offer a number of different styles of head attachments for their gas trimmers. However, these attachments can fit onto other gas trimmers provided that a few key measurements match up. So, whether you’re upgrading to a better attachment or the old attachment broke, find these measurements and you can replace it for a Ryobi attachment.
Head Arbor Bolt
The arbor bolt on the head connects the head to the gearbox on the end of the shaft. This bolt is at the center of the head, on the inside, and comes in either a “male” or “female” attachment, depending on the bolt on the receiving end of the trimmer. These bolts must match perfectly if the Ryobi head is going to be used on another gas trimmer. If these bolts don’t measure precisely and match the gender, the head won’t connect to the driveshaft and the head won’t spin.
Matching Arbor Bolts
This arbor bolt is measured in several ways. Two of these are the diameter of the bolt and the number of threads on the screw end of the bolt. On the trimmer head’s package, a string of numbers will account for these measurements. They will often state the bolt diameter, for example, 5/8-inch, and will also have a number beside the diameter, which is the thread count of the bolt; for example, a common thread count is 25.
Gender and Rotation
The gender of the bolt must match the replacement head’s bolt. Gender is subscribed as either male or female, and will be the opposite of the receiving end of the trimmer. The rotational direction, either clockwise or counterclockwise, must match the trimmer’s rotational direction. For example, if a trimmer has a counterclockwise thread with a female receiving end, it will need a trimmer head that also uses a counterclockwise thread, but with a male arbor bolt. The rotational direction will be abbreviated on the package as either LH or RH for left-hand thread and right-hand thread, respectively. The gender will be marked as either F or M for male or female respectively.
Using Bolt Adaptors
If the arbor bolts on the Ryobi attachment don’t match with the other gas trimmer, it may be possible to use a bolt adaptor to match them up. The bolt adaptors can change the four different dimensions described previously. For example, the bolt adaptor can change a left-hand male thread into anything that will require it to match the nut on the trimmer. Adaptor bolts may come with the head attachment; if not, they can be purchased from a home and garden store.