Some things to keep in mind when sizing bolts for ANSI flanges: 1. What pipe diameter and ANSI class is being used? This determines bolt count and diameter. 2. How thick is the gasket in between the flanges? This determines the bolt length. 3. Will there be an insulation kit between the flanges? This determines the bolt length. 4. Add extra 1​/​2" to bolt length to make sure the threads protrude on both sides. 5. What kind of finish is needed on the bolts? 6. Spiral wound gaskets can only be used once. 7. Bolts can only be used once after they are torqued. 8. To avoid bolt or flange damage, use a [flange alignment kit](https://trunkline.com/?q=flange+alignment). 9. Use a flange bolt torque specification for torque values and torque sequence. 10. Use two-holed flange arrangement when fitting flanges together. 11. Use a [bolt chart](http://www.rjsales.com/products/ansi_flanges/misc/e.html ) or [bolt table](https://www.texasflange.com/products/flange-dims-weights/bolt-and-stud-dimensions-asme-b16-5-flanges/ ) to calculate dimensions. 12. Leave enough room on both sides of flanges and valves for bolts to slide in and out (don't weld obstructions too close to flange bolt holes)