If a firearm transferee’s identification lists something other than male or female for their gender, what should they check on question 14 of Form 4473?

If a transferee’s identification states anything other than male or female, such as “X”, the transferee should check “Non-Binary”. The ATF Form 4473 instructions to question 14 state, “Individuals with neither male nor female on their identification document(s) should check Non-Binary.”