In one example, a group of printing fluid cartridges in which each cartridge includes: a reservoir; a printing fluid outlet from the reservoir; multiple electrical contacts arranged next to one another across the cartridge with an interface along the cartridge between each pair of adjacent electrical contacts; and multiple guideways next to the electrical contacts lengthwise and configured to align the cartridge to a receiver when the cartridge is installed in the receiver. Each of the guideways spans exactly one of the interfaces widthwise and is configured to simultaneously align the electrical contacts to corresponding electrical contacts on a receiver and to discriminate the cartridge from other printing fluid cartridges to prevent the cartridge from being inserted incorrectly into a receiver.