The sleeve of Muff coupling is designed as a

Explanation:

Muff coupling:

• Muff coupling is also called sleeve coupling or box coupling. It is a type of rigid coupling. It consists of a sleeve or a hollow cylinder, which is fitted over the ends of the input and output of the shaft by means of a sunk key.
• It is the simplest form of coupling with only two parts sleeve and key. It is simple to design and manufacture.
• It has no projecting parts except the key head. The external surface of the sleeve is smooth. This is an advantage from the standpoint of safety to the operator.
• It has a compact construction with small radial dimensions.
• It is cheaper than other types of coupling.
• The sleeve of Muff coupling is designed as a hollow shaft.
• Muff coupling is difficult to assemble or dismantle. The sleeve has to be either shifted over the shaft by half of its length or the ends of the shafts have to be drawn together or apart by half-length of the sleeve.