Section 4. The examiners may make rules as they consider proper for the performance of their duties and shall promulgate rules and regulations governing the qualifications of applicants for examination. They shall examine each applicant desiring to engage in the business of a master plumber or a journeyman plumber, as to his practical knowledge of plumbing, house drainage, plumbing ventilation, and gas fitting. They shall examine each applicant desiring to engage in the business of a master gas fitter or a journeyman gas fitter as to his practical knowledge pertaining to gas fitting, natural and manufactured gas and the installation of undiluted liquefied petroleum. They shall examine each person who applies to be licensed as an undiluted liquefied petroleum gas installer, and each person who applies to be licensed as a limited undiluted liquefied petroleum gas installer. They shall subject each applicant to a practical test satisfactory to the examiner, who, if satisfied of his competence, shall issue to him a license as applied for. They shall hold frequent examinations in the city of Boston, and also at such other convenient places within the commonwealth as they deem necessary. Public notice shall be given of all examinations. Every application for examination shall be in the handwriting of the applicant who shall be notified by the examiners of the time and place of examination. The examiners may, without payment of any fee, issue a probationary license in force for six months to a person who, having worked as an apprentice, or under a verbal agreement for instruction, for not less than three years, presents an application therefor with the signed endorsement of his employer agreeing to be responsible for all work done under the license and to have the licensee, at the expiration of the license, present himself for examination as a journeyman.

They shall grant a credit of five per cent to the examination standing of each applicant who is a veteran, as defined in clause Forty-third of section seven of chapter four. The examiners shall promulgate regulations to determine the allowable education and work hour credits for veterans and military personnel.