The Prop-Jack is a purpose-built spring-loaded brace jack engineered for luthiers who need to re-glue loose or cracked guitar braces and soundboards without removing the top. Turned from tough, low-friction POM, each jack expands from a compressed length to a fully extended position and locks under spring tension, exerting constant, even pressure while the adhesive cures. A cross-cut saddle on one end bites into the brace to prevent side-slip, while the opposite magnetic tip pairs with any steel caul or rare-earth magnet placed on the exterior, letting you locate hairline cracks and clamp them dead-center. Available in three overlapping lengths, the tapered body offers a positive grip for fine-tuning compression inside dreadnoughts, OM, parlor or classical bodies alike