To determine whether the Promis "KG300" is compatible with Swiss gas cylinders such as Vitogaz or Socar, and whether it is ready for a gas hose with a 1/4" screw, here are a few things to consider:

1. Compatibility with Swiss gas cylinders: Swiss gas cylinders, such as those from Vitogaz or Socar, generally use specific fittings. It is important to check whether the "KG300" is designed to accept these types of fittings. You should consult the product manual or contact the manufacturer for precise compatibility information.

2. Ready for gas hose with 1/4" screw: Most gas appliances are designed to accept hoses with standard fittings. A 1/4" screw is a common type of fitting, but check that the "KG300" is specifically designed for this type of connection. Again, consulting the manual or contacting Promis for confirmation is recommended.

In short, for a precise answer, it is advisable to contact the manufacturer directly or consult the product's technical documentation.