This is a standard #13 O-ring which is used with “propsavers”. This size works great with our 17-gm and 24-gm motor. Its a little too big for our 10gm motors. This sale is for 8 pieces (EIGHT O-rings).
O-rings do degrade with time outside, they will quickly develop cracks from sun exposure. Inspect them often and its best to use fresh ones each time you go flying. Fortunately they aren’t expensive! Since this is such a small item we recommend combining it with other items in your cart.