I sometimes have what looks like a white thread in my stool, sometimes i only see 1 or a few, once i saw many. i don't know if it's fibers or pinworm?

Itching: If there is no itching around you anus, especially at night, the "white threads" are not likely to be pin worms. It is nor feasible to say what those may be without a stool examination If you do not have any symptoms, did not travel outside the USA, you may ignore these. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex.

Likely not: As an adult,you acquire pin worms by ingesting the eggs when they get on your hands caring for in infected toddler. The worm lays its eggs around the anal opening and the glue like material that holds the eggs produces a skin reaction/itching. Most adults pass thread like debris as byproducts of veritable intake, since humans do not digest some of the cellulose that accompanies these foods.