Mike M. What is AS568? AS568 is the standard that defines o-ring sizes in the United States. Every standard o-ring you’ll encounter in American engineering has a “dash number” (like -214 or -028) that maps to specific inner diameter (ID) and cross-section (CS) dimensions. The dash number tells you everything: First digit = cross-section series (0XX = … Read more
What is a Static O-Ring Seal? A static o-ring seal is one where the o-ring doesn’t move during operation — it just sits in a groove and gets compressed between two mating parts. Think flanges, covers, manifolds, and housings. If you’re not familiar with standard o-ring sizing, start with AS568 O-Ring Sizes first. These guidelines … Read more
Why Hardness Matters Hardness testing is the quickest way to verify a material’s heat treatment and estimate its tensile strength without destroying the part. In practice, you’ll encounter three scales constantly: Brinell (HB), Rockwell B (HRB), and Rockwell C (HRC). Conversion Table — Steel These conversions are approximate and apply to carbon and alloy steels. … Read more
Geometric Dimensioning & Tolerancing (GD&T) GD&T is the language of engineering drawings. If you’re reading prints or designing parts, you need to understand these symbols. This reference covers the 14 geometric characteristic symbols defined in ASME Y14.5, with explanations and tolerance zone definitions. GD&T replaces ambiguous plus/minus tolerancing with precise geometric controls. Instead of saying … Read more
Metric Hex Bolt Head Dimensions When working with metric fasteners, the wrench size (width across flats) follows a different pattern than US bolts. Here’s the quick reference: Bolt Size Width Across Flats (mm) Width Across Corners (mm) Head Height (mm) M5 8 9.24 3.5 M6 10 11.55 4.0 M8 13 15.01 5.3 M10 16 (or … Read more
NPT Tap Drill Sizes When tapping NPT threads, the drill size determines the minor diameter of the internal thread. Because NPT threads are tapered, the drill creates a straight hole that the tapered tap gradually engages — you’ll get full threads near the entrance and partial threads at depth. NPT Size TPI Tap Drill (in) … Read more
The Complete Drill Size Reference Why does this chart exist? Because someone at some point decided that drill bits should come in four completely different naming systems — fractional inches, letter sizes (A–Z), number/gauge sizes (#1–#97), and metric. And engineers need to convert between all of them constantly. This master chart lists all standard drill … Read more
Why Surface Finish Matters Surface finish (or surface roughness) describes the texture of a machined surface. It affects sealing, wear, fatigue life, coating adhesion, and appearance. If you’re designing parts that mate, seal, or slide against each other, you need to specify surface finish on your drawing. Common Surface Finish Values Ra (µin) Ra (µm) … Read more
What is NPT? NPT (National Pipe Thread) is the US standard for tapered pipe threads. The taper is 1°47′ (3/4 inch per foot), which means the threads wedge tighter as you screw them together — creating a seal. NPT threads require thread sealant (Teflon tape or pipe dope) for a leak-free connection. NPT vs. NPTF: … Read more
Matching Nut Grades to Bolt Grades Using the wrong nut with a high-strength bolt is a surprisingly common mistake — and it’s dangerous. A Grade 5 nut on a Grade 8 bolt will strip the nut threads before the bolt reaches its rated clamp load. Always match (or exceed) the nut grade to the bolt … Read more