You only need glue records when the hostname for your nameserver is part of the same domain as it's trying to serve.
Glue records are published in the parent zone. Hence if the operator of
example.com wanted to have nameservers named
ns2.example.com then the
.com domain would need something like:
example.com. IN NS ns1.example.com.
IN NS ns2.example.com.
ns1.example.com. IN A 192.0.2.1
ns2.example.com. IN A 198.51.100.5
(example subnets taken from RFC 5737).
The child zone would usually have the same A records in it (even if only for consistency), but when they're in the child zone they're not technically glue records any more.