Thank you for you inquiry, John111! The red/blue indicator button for the Delta Foundations Lavatory B510LF faucet is not sold separately from the full handle RP42986. Please see the Parts Diagram link for this faucet below. https://media.deltafaucet.com/PartsDiagram/DPD-L-B501LF.pdf Best regards, Tanya

Thank you for your question, Rob. This button is designed to fit the 521-ECO-DST-A faucet. The diameter of the exterior insert on the button is just over 1/4" (.268") and the depth is 3/20". The overall diameter of the face is 0.33" and the overall depth including the face is 1/5". Best regards, Jon