Its primary features are two pieces of a durable material, attached as back and seat to one another at a 90° or slightly greater angle, with usually the four corners of the horizontal seat attached in turn to four leg and a shaft about which a four-arm turnstile on rollers can turn—strong enough to support the weight of a person who sits on the seat The legs are typically high enough for the seated person’s thighs and knees to form a 90° or lesser angle.