I created caps to allow for on-the-knee exercises with adjustable dumbbells without discomfort. Using these will prevent you from experiencing pain from the shaft. This listing is for a set of 2 caps (dumbbells not included). I have sold over 180 sets so far. If the caps break within 2 weeks of use, provided the usage instructions are followed, I will replace them free of charge. The size is slightly smaller than a 1.25kg plate to prevent damage. I use IROTEC screw-type dumbbells, but I believe these will work with 28mm screw-type dumbbells. I was able to use 3-4 plates, including the collars. * The screw part needs to be exposed about 1.5cm for installation. Each cap weighs approximately 70g. The material is durable ABS. I have been using them for about six months without any damage (with a weight of about 25kg, used every other day). These are handmade, so please understand that there may be small burrs, dents, or scratches. ☆ Usage Instructions ・Although the photo shows the dumbbells standing upright, please do not do this as it may cause injury or damage. ・Do not overtighten the caps, as this may cause damage. ・Do not drop the dumbbells, as this may lead to damage. ・Do not use the caps themselves as collars, as this is dangerous. ・Avoid direct sunlight, as it will accelerate the deterioration of the material. ※ I cannot offer discounts on this product. ※ Please be aware that I only sell this product on Mercari.