Procomp Electronics billet main caps are precision CNC-machined from superior-quality 1025 billet steel. They come available as stock replacements (straight bolt) or with splayed outer bolt holes. The splayed caps feature 10 degree angled outer holes to positively reinforce and tie the block together. These extreme main cap sets consist of the center four caps. Procomp Electronics billet main caps improve reliability in highly stressed engines by reducing distortion of the main bearing bores, and increasing the cap's resistance to closing up under high loads.