Features: 1.Plastic + Metal: Guitar tuning knob is made of excellent plastic + metal materials, giving you a better feel and experience 2.Basic s: This guitar tuning has elegant appearance, and the mounting hole size is approximately (L x W) 3.8mm?4mm 3.Scope of Application: This is a tuning button, which is suitable for electric guitars, folk classical guitars, etc. 4.Stable Performance: Tuning knob is environmentally friendly, odorless, sturdy and durable, stable in performance, and long in service life 5.Exquisite Workmanship: Fine workmanship guitar tuning, with good texture, glazed appearance and easy to use specification:Item Type: Tuner Machine Head Buttons Material: Plastic + Metal PackageList: 12 x Tuning knob 12 x Screw 12 x Black Spacer 12 x White Spacer NoteOnly approximate size for this tuning knob mounting hole for reference, can not be totally exact.Only the approximate for reference. Customers can be be sure if this mounting hole is too big to install according to this size. But if the mounting hole is too small for you, would be hard to fit in. If so, please enlarge the hole with small file. So that this problem can be saved. Please check all very carefuly before order. Thanks for your cooperation.