A clamping system for clamping a printing screen frame (6, 93, 94) within a printing machine during a printing process, comprising: a receptacle for receiving a printing screen frame (6, 93, 94) in use, the receptacle at least partially defining a space for accommodating the printing screen frame (6, 93, 94), and the receptacle including a frame support (43a, 43b) for supporting the printing screen frame (6, 93, 94) in use, a clamping bracket (36a, 36b, 90), a first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) retained by the clamping bracket (36a, 36b, 90), the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) bearing an engagement surface (54, 62, 66, 70, 102, 112, 122, 132), and a fluid supply for supplying fluid to the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) to inflate it from an uninflated state to an inflated state, wherein during inflation of the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) the engagement surface (54, 62, 66, 70, 102, 112, 122, 132) is caused to move towards said space so that in use, while the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is in the uninflated state a printing screen frame (6, 93, 94) is loaded into the receptacle, and while the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is in the inflated state the printing screen frame (6, 93, 94) is clamped by the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) to be stationary relative to the frame support (43a, 43b), the clamping bracket (36a, 36b, 90) comprising a channel of substantially U-shaped cross-section, having a base (47, 82a, 82b) and two opposing sidewalls (48a, 48b, 83a, 83b, 84a, 84b), characterised in that the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is attachable to the base (47, 82a, 82b) of the channel, and is laterally restrained by the sidewalls (48a, 48b, 83a, 83b, 84a, 84b) of the channel during inflation. a receptacle for receiving a printing screen frame (6, 93, 94) in use, the receptacle at least partially defining a space for accommodating the printing screen frame (6, 93, 94), and the receptacle including a frame support (43a, 43b) for supporting the printing screen frame (6, 93, 94) in use, a clamping bracket (36a, 36b, 90), a first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) retained by the clamping bracket (36a, 36b, 90), the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) bearing an engagement surface (54, 62, 66, 70, 102, 112, 122, 132), and a fluid supply for supplying fluid to the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) to inflate it from an uninflated state to an inflated state, wherein during inflation of the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) the engagement surface (54, 62, 66, 70, 102, 112, 122, 132) is caused to move towards said space so that in use, while the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is in the uninflated state a printing screen frame (6, 93, 94) is loaded into the receptacle, and while the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is in the inflated state the printing screen frame (6, 93, 94) is clamped by the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) to be stationary relative to the frame support (43a, 43b), the clamping bracket (36a, 36b, 90) comprising a channel of substantially U-shaped cross-section, having a base (47, 82a, 82b) and two opposing sidewalls (48a, 48b, 83a, 83b, 84a, 84b), characterised in that the first inflatable bladder (46, 60, 68, 72, 100, 110, 120, 130) is attachable to the base (47, 82a, 82b) of the channel, and is laterally restrained by the sidewalls (48a, 48b, 83a, 83b, 84a, 84b) of the channel during inflation.