According to Official Guinness Records,
The longest duration holding an iron cross position on Roman rings was 39.23 sec by Zak Kerkoulas (USA) at the Field House at Chelsea Piers in New York, New York, USA, on 27 August 2010. A proper iron cross requires the body to be rigid with arms at a 90-degree angle to the body and parallel to the floor.
Witnesses included former All-American collegiate gymnast Ramiro Mora and former USA national gymnastics team member on the rings Chris LaMorte.
For a complete list of 2010 records, please visit 2010 Guinness Records in United States.