Here’s a link to purchase the knobs on Amazon-
Strength, durability, and heat resistance are some of the benefits of this broad range of phenolic handle. Extremely versatile range of mountings. Female insert machined to suit. Mounting type: female insert. Thread length/depth: 3/8″. Mounting diameter and threads per inch: 1/4-20. Plastic material: thermoset; insert material: brass. Measures 7/8″ diameter by 2-41/64″ height.
One of each of the following that can be found at any self respecting Hardware Store. This one was Ace Hardware at Gloucester Crossing.
1-1/4 Diameter 1/4-20 Female thread general purpose ball knob.
1/4-20 1 inch hex bolt.stainless
1/4 lock washer stainless
1/4-20 nut stainless
1/4 inch drill bit. Go slow. Once drilled feed the bolt through the drilled lid vent tab, then slide the lock washer and next the nut. Tighten and then screw the ball knob on. Done.