1) A spike or small nail, although the exact meaning is uncertain.
The two examples found both occur in Ripon, with almost forty years between the references: 1354-5 In mercede fabri facientis pragges et lokats de ferro suo pro proprio pro fenestris figendis, 8d, Ripon
1391-2 In vj pragges ferri emp. pro dictis domibus, 2d, Ripon. A connection with ‘brag’ is unlikely, since these were ‘great’ nails, so perhaps it is an early form of ‘prog’ for which there is evidence from 1615 in the sense of ‘skewer’.