Opinion by

William Kerr’s Sons, one of the defendants, contracted with the First National Bank of Connellsville to erect a bank building and the plaintiff contracted with them in writing to furnish the materials for and to do all the brick work. By the terms of the contract the plaintiff was to furnish “all materials and labor required for all the brick work on the First National Bank Building — specified and shown on plans prepared by Mowbray and Uffinger, architects, under the head of mason and brick work, or under any other heading, which is properly the above work.”

Whether under the fvgreement the plaintiff was required to lay the fireclay arches, lintels and roof coping was a subject of dispute at the trial, and parol testimony was admitted to show the mutual understanding of the parties as to the meaning of the contract at the time it was signed and to show by persons familiar with the business the meaning of the words “ properly brick work ” when used in a building contract such as this. The assignments of error to be considered relate to the admission of this evidence.

If the intention of the parties could have been ascertained from the specifications, there would have been nothing to explain by parol evidence. These specifications were prepared to designate not the work to be done by the plaintiff, but all the work to be done by the principal contractor on the whole building. There was a general classification of the work but not one in which under separate heads all of a specific kind of work and only work of that kind Avas included. Brick work is found under three distinct heads, and under the head of “ brick work ’•’ in immediate connection with the laying of fireproofing is found work provided for under different heads. The obligation of the plaintiff to do all of the brick work under whatever head named Avas made clear by the agreement, but what was “ properly brick work ” was not. It was therefore competent in aid of the construction of the writing to prove the understanding of the parties at the time in respect to it and to ex*549plain the trade meaning of a technical term used in connection with the particular work which was the subject of the agreement : Brown v. Brooks, 25 Pa. 210; Carey v. Bright, 58 Pa. 70.

The judgment is affirmed.