[Mini DC Voltmeters]Total 20PCS, 4 colors combined(4PCS Red/Yellow/Blue/Green/White); 0.28 inch LED Panel; small in size and light in weight; wire is made of 28awg gauge; install the hole: 23 x 10 mm [2 Connection Methods]3 wires are connected separately to measure voltage and power(Red yellow is both for pos, black is ); 3 wires are used as 2 wires, connected to measure voltage(Red and Yellow can be paired for pos, black is ) [Features]Reverse polarity protection, voltmeter 't burn out if reverse polarity is applied; high precision; low starting working voltage; fine adjustment function [Note]Max voltage with yellow and red connected is 40V.To measure 40V (up to 100V) the yellow wire is connected to a separate voltage source that is 40V or less Colour:multicolor Material:led Package Contents: 20 x DC Voltmeter Display Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.