The main three parts of a scissor are the blade, handle and tensioner.
The blade edge is generally either bevel or convex. Bevel edge is the oldest design, the angle of the edge is steep and most durable. Serrations are sometimes added to help hold the hair, this can add a rough and noisy effect to the blade performance.
Convex blades are the more recent technology. This blade edge has a finer angle with a honed cutting line, it is also hollow ground, producing a smooth quiet cutting action.
Hairdressing Scissor handles come in 2 main styles, opposing or offset. Opposing finger holes are the traditional design with the finger and thumb travelling in the same plain which can get uncomfortable over time as the hand is not open. The more recent offset design allows you to cut with a more open hand, hence less hand and wrist fatigue.
The scissor tensioner allows you to make the necessary adjustments for optimum blade contact. Poorly adjusted scissors are a common reason for cutting issues. If the tension is to tight it increases blade resistance, pushes the hair and blunts the blade, to loose and the hair will bend or fold and the blades will connect unevenly. For optimum tension, hold the scissor by the thumb hole, blades fully open. Release the top handle, allowing gravity to close the blades. They should stop with around 10 to 20mm of travel left, depending on the scissor weight and length.