Using the prime factor circles on Polypad can help students make meaning of finding common factors of numbers. Below are two videos showing some ways in which students could find common factors (including the greatest common factor) of 336 and 1260.
Finding Common Factors Using Prime Factor Circles
Finding Common Factors Using Venn Diagrams
Further Reading
Greatest Common Factors – Divisibility and Primes
mathigon.org/course/divisibility/gcf