The abbreviations listed here are ones that you may see on drawings or other contract documents.
2/10 Rule: This rule states that the top of a flue must be at least two feet higher than any portion of the roof part within ten feet. Building codes usually have this rule or one similar to it in them.
4/1 Rule: A rule for safe placement of a ladder. The 4/1 rule states that for every four feet of working ladder length, the base of the ladder should be one foot out from the top support point.
4-inch Center: With regard to faucets, when the center of one handle to the center of the other handle is four inches with the spout between them. It is also referred to as 4" spread.
30 lb Felt: 30 lb felt was ...