O
Offering up
To temporarily hold a material or fitting in place to check its position, fixing points or to see how it looks.
Oilstone
A flat abrasive stone lubricated with oil or water, used for sharpening tools.
Olive
A metal ring used in plumbing to create a seal for brass compression joints.
One-piece-plastic joint block
Small plastic blocks used to create joints between two components, widely used in flat-pack furniture. For example, fixing a number of joint blocks approximately 1m (3ft 3in) apart to the inside face of a piece of plywood allows you to screw the plywood to a wall with its edge abutted against the wall.
Opaque
A material or substance through which light cannot pass.
O-ring
Plastic ring or gasket for sealing pipe joints, like a washer.