Bohning's A Nock fits small diameter shafts with an ID of .204" (commonly known as 5mm or X Nock). The A Nock features a double-lock throat and raised index. Its throat size is .120" (3.05mm), and each A Nock weighs an average of 7.0 grains (453.6 mg). Tech tip: for easier insertion and indexing, apply a small amount of Bohning's Tex-Tite or Seal-Tite Wax to the nock shank. At Bohning, every nock style must pass the following steps before introduction to the market: 1. Computer simulations identify potential weak points. 2. Destructive testing methods expose possible design flaws or material defects. 3. Accelerated life cycle testing using a custom-built bow is performed at kinetic energy levels exceeding 110 ft-lbs (nearly twice that of most hunting bows). A single nock must withstand over 1000 shots or it goes back to step 1.