Protective sleeve for spark plug

A protective sleeve for a spark plug comprising:

• a center electrode;
• an insulator holding the center electrode therein;
• an attachment fitment holding the insulator therein and configured such that an attachment screw section that is screwed into an internal combustion engine is formed on an outer peripheral surface thereof;
• and
• a ground electrode that forms a spark discharge gap with the center electrode;
• wherein,
• a protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section,
• the attachment fitment includes a flange section on a base end side of the attachment screw section,
• the flange section has a diameter that is larger than that of the attachment screw section,
• the protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section,
• a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger;
• and
• a step section formed between the large diameter cylinder section and the main body cylinder section.