This is a self-made pressurized storage case for tennis balls, a pressure retainer to substitute for commercially available ball rescuers and ball savers. It uses a metal valve, so there's no worry of it coming off like rubber valves. (Important Notes) This product is shipped after confirming that there are no issues with the specifications by actually pressurizing the balls before packaging. Only the case is included; balls, air pumps, etc., are not included. When shipping, the case will be pressurized to 1.5 atmospheres to protect it. When using, release the air from the valve and open the lid. The lid can be easily opened and closed by holding the gray part and using a screwdriver, etc. (Photo 4). Opening and closing by holding the transparent case part will break it. When closing, refer to the position of the magic marker. Air can be easily added with a bicycle or car air pump; a pressure gauge is convenient. Before adding air, make sure that there is no sand or felt on the O-rings and screw parts, as this can cause air leaks. Air can be easily added with a bicycle or car air pump. Normally, new balls are 1.8 atmospheres. After using them once, pressurize them to around 1.8-2 atmospheres for about a week. The case has been tested up to 2.5 atmospheres. If tightening is not smooth, it is recommended to apply commercially available silicone grease to the screw part and O-ring. Sometimes the last ball is difficult to remove, but it can be easily taken out by hooking it with your fingernail. This is a handmade product, so please understand that there may be adhesive clouding, scratches, and dirt on the case that occurred during production. We cannot guarantee any damages caused by the use of this product, so please purchase with your understanding. 【How to Use】 If you use it frequently, it is recommended to use several storage cases. For reference, here's how I use it. At home, I use about 10 storage cases, writing the date of pressurization and the pressure on masking tape to rotate them to restore the ball pressure. On the day of practice, I take the storage case, air pump, screwdriver, and non-slip gloves in a shoe bag. With this method, the balls can be used until almost all the fuzz is gone. When I use it at home, I use the air pump from a puncture repair kit (photo) that is now standard equipment in recent cars. It's convenient.