Flat Iron vs Inside Skirt — What's the Difference?
Quick Answer
Flat Iron (flat iron steak) and Inside Skirt (inside skirt steak) are not the same cut: Flat Iron is chuck primal (Infraspinatus muscle, top blade of the shoulder clod); Inside Skirt is plate primal (Transversus abdominis muscle — the inner diaphragm muscle).
Canonical entities: Flat Iron · Inside Skirt
Side-by-side
| flat iron | inside skirt | |
|---|---|---|
| Primal | chuck | plate |
| Muscle / location | Infraspinatus muscle, top blade of the shoulder clod | Transversus abdominis muscle — the inner diaphragm muscle |
| Character | The second most tender muscle on the entire animal, after the tenderloin. A flat, rectangular steak extracted from the top blade by splitting it along the central connective tissue. Uniform thickness makes it ideal for grilling. Also known as butler's steak in the UK. | The 'other' skirt steak. Thinner, wider, and slightly tougher than the outside skirt (which is the standard 'skirt steak'). Most restaurant fajitas use inside skirt because the outside skirt is exported or sold at premium. Requires high heat, fast cooking, and slicing against the grain. |
Key differences
- Different primals: chuck vs plate.
- Texture and slicing: compare fibrous, grain-heavy cuts vs more tender steak-style muscles based on each cut’s description.
- Retail naming diverges by country—always map through a canonical cut when translating menus or labels.
When to use each
Flat Iron
Pick Flat Iron when you want its specific marbling/texture profile: The second most tender muscle on the entire animal, after the tenderloin. A flat, rectangular steak extracted from the top blade by splitting it along the central connective tissue. Uniform thickness makes it ideal for grilling. Also known as butler's steak in the UK.
Inside Skirt
Pick Inside Skirt when its primal/muscle traits fit the dish: The 'other' skirt steak. Thinner, wider, and slightly tougher than the outside skirt (which is the standard 'skirt steak'). Most restaurant fajitas use inside skirt because the outside skirt is exported or sold at premium. Requires high heat, fast cooking, and slicing against the grain.
Flat Iron and Inside Skirt are different canonical muscles/primals: Flat Iron is chuck (Infraspinatus muscle, top blade of the shoulder clod); Inside Skirt is plate (Transversus abdominis muscle — the inner diaphragm muscle).
Choose based on tenderness, marbling, grain direction, and how you plan to cook (sear vs braise vs slice thin).
Read the full guides: flat iron (what-is) · inside skirt (what-is) · flat iron hub · inside skirt hub