O-ring seals complement metal-to-metal backups in medium-pressure Fig. 100 unions, providing compressive sealing up to 1,000 psi. Nitrile O-rings in grooves on male subs energize under nut tightening, accommodating thermal expansion. For misalignment up to 7.5°, O-rings deform without failure, per API 6A Annex F. Viton O-rings for sour service resist swelling in H2S, maintaining https://globalsealstech.com/product/hammer-union-seal-2/