JLCMC Blog

Bearings & Housings

Sealed vs Shielded Bearings: What 2RS and ZZ Mean

Key Takeaways Suffix definitions: ZZ commonly means metal shields on both sides. 2RS commonly means seals on both sides, often contact seals. Always confirm the exact definition in the manufacturer's catalog. Design difference: A metal shield typically uses a non-contact clearance or labyrinth path at the inner ring, while a contact seal uses a sealing lip that contacts the mating surface, directly affecting contaminant exclusion and friction. "Sealed" variations: "Sealed" does not always mean "contac......

Sep 28, 2026

Selection Principles

NPT Thread Guide: Charts, Tap Drill Sizes, and Fitting Identification

Key Takeaways NPT (National Pipe Taper) is a U.S. standard tapered pipe thread defined by ASME B1.20.1: a 60° thread angle and a 1:16 taper on diameter, sealing through thread interference plus sealant. NPT tap drill sizes do not follow the diameter-minus-pitch formula used for straight machine threads — ASME B1.20.1 Appendix B provides guidance, and the tap manufacturer's data decides. The everyday sizes: 1/8 NPT (27 TPI, 0.405 inch major diameter), 1/4 NPT (18 TPI, 0.540 inch), 1/2 NPT (14 TPI, 0.84......

Sep 24, 2026

Fasteners & Hardware

Ball Nose End Mill Stepover: Scallop Height and Effective Diameter

Key Takeaways Geometric Control: Stepover directly controls geometric scallop height, but it does not automatically guarantee a measured Ra value. Cusp Height Formula: For a ball radius $R$ and pass spacing $s$ on a flat surface, the ideal cusp height is $h = R - \sqrt{R^2 - \frac{s^2}{4}}$. Tool Radius Advantage: A larger ball can use wider spacing for the same ideal cusp, provided it can reach the required geometry without gouging. Effective Diameter: The active cutting diameter near the tool tip ca......

Sep 23, 2026

Power Transmission

Roller Chain Size Chart: ANSI and BS Sizes in mm and Inches

Key Takeaways Identify the chain series first: ANSI and BS-series size codes belong to different dimensional families; changing the units does not change the chain type. Check four details together: Pitch, roller diameter, inner width and number of rows. Matching pitch alone is not enough to choose a replacement. Use the millimeter columns for comparison: Inch equivalents appear beside them, so there is no need to interpret two units in one cell. Count the gaps when measuring pitch: Six consecutive pi......

Sep 22, 2026

Selection Principles

Tap Drill Chart: UNC, UNF, Metric & NPT Drill Sizes

Key Takeaways A tap drill creates the hole a tap cuts internal threads into; the drill diameter controls how much full thread the finished hole has. For Unified inch threads, drill size = major diameter − 1/TPI (rounded to the nearest standard drill) is a commonly used starting point for approximately 75 percent thread engagement; the actual percentage depends on thread geometry and the specified hole tolerance. For metric threads, the quick formula is drill = thread diameter − pitch in millimeters, r......

Sep 21, 2026

Fasteners & Hardware

Manual SMT Stencil Printer Sizing: Print Area, PCB Support and Frame Fit

Key Takeaways Different dimensions: Worktable size, effective print area, board envelope, and stencil frame size are different dimensions. Check the full pattern: Check the whole aperture pattern in its intended orientation, including clearance for the printing stroke. Thickness is not enough: A compatible board thickness does not prove that a populated underside or a support fixture will fit. Support and contact: Stable support and close stencil-to-board contact are necessary for a repeatable printin......

Sep 19, 2026