Knurled nuts, bezel nuts, toggle switch nuts. There a tool: https://www.stewmac.com/luthier-tools-and-supplies/types-of-tools/wrenches/adjustable-toggle-switch-wrench.html?utm_source=google&utm_medium=shopping&utm_campaign=2020-07-gp&gclid=Cj0KCQjwpNr4BRDYARIsAADIx9wR8YpzbH94q6RjErK2bSE1Mi10SzTen6Icdbx1creIlH2B6euJkXkaAtoKEALw_wcB
Don C