| Battens | Horizontal roof timbers giving intermediate bearings to the slate | |
| Boards | Horizontal roof timbers giving intermediate bearings to the slate | |
| Broad Ladies | Historical name for 16" x 9" slate. Metric equivalent 400x230 | |
| Capital | Welsh Slate thickness 6mm slate +/- 2mm | |
| Celtic | Welsh Slate thickness 10mm slate +/- 2mm | |
| Countesses | Historical name for 20" x 10" slate. Metric equivalent 500x250 | |
| County | Welsh Slate thickness 8mm slate +/- 2mm | |
| Cwt-y-Bugail | Quarry near Blaenau Ffestiniog | |
| Dark Blue Grey | Colour of slate from Cwt-y-Bugail Quarry | |
| Dark Grey | Colour of slate from Blaenau Ffestiniog Quarry | |
| Diminishing Course | Practice of having smaller length slates higher up the roof | |
| Double | Historical name for 12" x 10" slate. Metric equivalent 300x250 | |
| Dressing | Cutting a slate down to a set size | |
| Duchesses | Historical name for 24" x 12" slate. Metric equivalent 600x300 | |
| Eaves Slates | Slates on the lower edge of the roof | |
| Ffestiniog | Quarry in the town of Blaenau Ffestiniog | |
| Gauge | Length of slate - headlap divided by 2 | |
| Headlap | The portion of slates covered by two other slates | |
| Heather Blue | A Penrhyn Quarry material colour | |
| Heather Grey | A Penrhyn Quarry material colour | |
| Holing Gauge | Distance from the tail of slate to the nail holes. Holing gauge = gauge + lap + 8 to 15mm | |
| Ladies | Historical name for 10" x 8" slate. Metric equivalent 250x200 | |
| Marchionesses | Historical name for 22" x 11" slate. Metric equivalent 550x280 | |
| Margin | The exposed area of a roofing slate | |
| Narrow Ladies | Historical name for 14" x 7" slate. Metric equivalent 350x180 | |
| Penrhyn | Quarry in the town of Bethesda | |
| Pitch | Angle of slope on a roof | |
| Princesses | Historical name for 24" x 14" slate. Metric equivalent 600x350 | |
| Rag Slates /Queen rag slates | Large random width diminishing length slates normally from 40" down to 26 long | |
| Random Slates | Traditional roof design with slates varying in length and width and laid in diminishing courses. Generally accepted as the most attractive slate roofs. | |
| Slate & a Half | Slate one and a half times the width of a standard slate, typically used at verges and abutments | |
| Small Duchesses | Historical name for 22" x 12"slate. Metric equivalent 550x300 | |
| Small Ladies | Historical name for 14" x 8" slate. Metric equivalent 350x200 | |
| Top Slate | Short course of slates to finish the roof below the ridge | |
| Viscountesses | Historical name for 18" x 9" slate. Metric equivalent 450x230 | |
| Wide Ladies | Historical name for 16" x 10" slate. Metric equivalent 400x250 |