Single layer gear, additionally referred to as spur gear, is straightforward and direct transmission, and most of the shafts are heavily matched.Gear outer diameter=(number of teeth+2) * 0.5 (unit: mm)For example, 20-2A signifies that the number of tooth is 20, and the diameter of the tools is two mm. A signifies that it is closely matched with the 2mm shaft. If it's B, it skill it is loosely matched with 2mm shaft.Product Description:Name: Plastic Shaft Single Layer GearsModel: 0.5MMaterial: PlasticUsed:Do DIY science and small production, product design, mechanical model.Remarks: If you've special needs, please contact us, we can customize per your needs!The data is measured manually, for reference only, please talk to the genuine object!Package Include:According for your Choose!