# Understanding .hdb format **URL:** \ **Category:** User discussions\ **Tags:** forcefield\ **Created:** [February 5, 2025, 5:09pm UTC](https://gromacs.bioexcel.eu/t/understanding-hdb-format/11473 "2025-02-05T17:09:28Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![ganesh7shahane](https://avatars.discourse-cdn.com/v4/letter/g/51bf81/32.png) [@ganesh7shahane](https://gromacs.bioexcel.eu/u/ganesh7shahane)\ **Post date:** [February 5, 2025, 5:09pm UTC](https://gromacs.bioexcel.eu/t/understanding-hdb-format/11473/1 "2025-02-05T17:09:28Z")
GROMACS version: Any GROMACS modification: No I am trying to add a new residue to the Amber ff14Sb force field, and as a part of it I am trying to add all the residue’s hydrogens to the force field’s aminoacids.hdb database. Can anybody help me understand what the number in the second column (red rectangle) means or represents for the following example of THR residue? ![theronine_hdb](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/5/5b569f0944c7898f505480a59b58551fc95c040c.png) This will help me add the necessary numbers for the new residue. ---
**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\ **Post date:** [February 6, 2025, 8:31am UTC](https://gromacs.bioexcel.eu/t/understanding-hdb-format/11473/2 "2025-02-06T08:31:37Z")
Hi, here you might find some answers [https://manual.gromacs.org/2024.5/reference-manual/topologies/pdb2gmx-input-files.html](https://manual.gromacs.org/2024.5/reference-manual/topologies/pdb2gmx-input-files.html) I hope it helps \Alessandra ---
**Author:** ![ganesh7shahane](https://avatars.discourse-cdn.com/v4/letter/g/51bf81/32.png) [@ganesh7shahane](https://gromacs.bioexcel.eu/u/ganesh7shahane)\ **Post date:** [February 6, 2025, 10:22am UTC](https://gromacs.bioexcel.eu/t/understanding-hdb-format/11473/3 "2025-02-06T10:22:06Z")
Thanks Alessandra, this was very helpful!