It contains two grooves (one groove size is 88 x 60 mm), which is the right size to fit a 400 holes breadboard; the other groove is for the Arduino UNO., Max. Whadda WSG135: Soldering kit, DIY, electronic decision maker, yes/no The project holder allows you to attach the Arduino® UNO and the included breadboard together. breadboard size: 88 x 60 mm , Dimensions: 160 x 106 mm , Weight: 50 g Kit Maker Organizador WHADDA Anfängerset Für Arduino WPK501 Kit Maker Electrónica WSAH4700 Kit Protector Altifalante WHADDA | Viptrónica The position of 4 M3 screw holes fits the Arduino UNO mounting holes.