A pork ham comes apart into three big boneless muscles: the inside, the outside and the knuckle. USDA's pork spec, IMPS Series 400, gives each one its own item number.
| Inside | Outside | Knuckle | |
|---|---|---|---|
| USDA spec | IMPS 402F, leg, inside | IMPS 402D, leg, outside | IMPS 402H, leg tip |
| Share of a ham | 16.1% | 17.6% | 9.8% |
| Median print, 5 years | 155¢/lb | 157¢/lb | 158¢/lb |
| Loads, last 12 months | about 890 | about 770 | about 770 |
The inside is taken off the leg along its natural seam, with the bones, cartilage and heavy connective tissue removed. The outside is the group of outside muscles, and a buyer can ask for its eye to come off as a separate item, 402K. The knuckle is the leg tip, and USDA's spec says it "may also be referred to as a Knuckle." When all three are boxed together, USDA calls it a 3-way boneless leg, 402G.
In a 2016 Market News paper, USDA put the three muscles at about 43 percent of a ham's weight. Most of the rest is bone, skin, fat, shank and trim.
To blue and red
These words say how far a muscle is trimmed. USDA's spec calls the thin membrane on a seamed muscle "silver" or "blue" tissue. A muscle trimmed to blue has its fat taken off down to that membrane, so the membrane shows.
In the trade, trimmed to the red goes one step further: the membrane comes off too, and the red lean shows. USDA's spec has the same step, called surface membrane removed, with at least 90 percent of the surface showing lean.
USDA prints a separate (red) combo line for each muscle, and those lines cost more. Over the five years to October 2026, on days both printed:
| Plain | (red) combo | (red) higher on | |
|---|---|---|---|
| Insides | 155¢/lb | 177¢/lb | 88% of days |
| Outsides | 157¢/lb | 182¢/lb | 93% of days |
| Knuckles | 159¢/lb | 187¢/lb | 89% of days |
The median gap was 11 percent on insides, 14 on outsides and 17 on knuckles. The (red) lines are also combo lines, packed in bulk bins, and the prints do not split how much of the gap is trim and how much is pack. USDA's item names do not say how the plain lines are trimmed, so ask on a plain quote.
No muscle leads
Over five years the three plain lines priced close together, with medians of 155, 157 and 158 cents. Day to day they still differ, by a median of 8 cents a pound from highest to lowest, and no one muscle holds the top. The knuckle printed highest on 42 percent of days, the outside on 34 and the inside on 24.
Muscle ham to blue
USDA also prints a boneless ham made of several muscles, trimmed to blue. Until March 2026 it was one line, muscle ham to blue. Since April 2026 USDA has printed it as a 3 muscle and a 4 muscle ham. The 3 muscle carried about 300 loads from April to late October, and the 4 muscle only a handful. On days both printed, the 3 muscle ham ran a median 16 percent over plain insides, and it was higher on 98 percent of those days. USDA's 2016 paper put a 3 muscle ham at about 43 percent of a ham's weight and a 4 muscle at about 46 percent.