Chain tensioner

A chain tensioner comprising:

• a tubular cylinder having a bottom;
• a tubular plunger axially slidably inserted in the tubular cylinder, the tubular plunger having an open end inserted in the tubular cylinder, and a closed end protruding beyond the tubular cylinder;
• an internal thread on an inner periphery of the tubular plunger;
• a screw rod including, on an outer periphery of the screw rod, an external thread threadedly engaged with the internal thread;
• and
• a return spring disposed between the screw rod and the tubular plunger, and configured to bias the tubular plunger in a direction in which the tubular plunger protrudes from the tubular cylinder,
• wherein the internal thread comprises:
• a push-in-side flank configured to receive pressure when a load that tends to push the tubular plunger into the tubular cylinder is applied;
• a protruding-side flank configured to receive pressure when a load that tends to cause the tubular plunger to protrude from the tubular cylinder is applied;
• and
• a thread top face between the push-in-side flank and the protruding-side flank,
• wherein the push-in-side flank has a first flank angle which is an angle defined between a surface of the push-in-side flank and a vertical axis,
• wherein the protruding-side flank has a second flank angle which is an angle defined between a surface of the protruding-side flank and the vertical axis,
• wherein the first flank angle is larger than the second flank angle,
• wherein each of the push-in-side flank and the protruding-side flank of the internal thread comprises a rolled surface having a surface roughness smaller than Ra_1.0 μm, and
• wherein the internal thread further includes, at a position of the internal thread at which the protruding-side flank intersects with the thread top face, a chamfer configured to receive a bulge resulting from excess materials pushed out from the protruding-side flank during formation of the internal thread by rolling.