WESTport Tri-Roll Comparators (External)

EXTERNAL THREAD COMPARATOR

Tri-Roll Comparators (External)

The Tri-Roll is WESTport's flagship external thread comparator — three gaging rolls give a live pitch-diameter reading across the widest size range (frames #0–12). Build your system below: frame, base, dial indicator, gaging rolls for your thread, and a master setting plug.

Request a Quote
ISO/IEC 17025Accredited Calibration
ISO 9001Certified Quality Management
ANSI/NCSL Z540-1Accredited Calibration Lab
Made in USASince 1989

What goes into a Tri-Roll system

  • 1. Frame

    Holds the rolls and indicator. Sized by capacity, frames #0–12 (each covers several thread sizes).

    One-time

    Shop frames 

  • 2. Gaging Rolls

    The measuring elements — a set of three, specific to your thread size, pitch, and type (3/4/5).

    Per thread size

    Shop gaging rolls 

  • 3. Dial Indicator

    Reads pitch-diameter variation. Choose your graduation. (Also used on STC.)

    One-time

    Shop indicators 

  • 4. Base & mounts

    Bench base, dual-frame base, mounting bar, hand-held handle.

    One-time

    Bases & mounts 

  • 5. Master Setting Plug

    Calibrated reference that zeroes the gage before you measure. One per thread size.

    Per thread size

    Setting plugs 
1 5

How do you want to shop?

  • Building a complete system?

    You'll need a frame, base, indicator, a set of gaging rolls for your thread, and a master setting plug. Start with your frame size below.

    Start with frames 

  • Adding a new thread size?

    Order gaging rolls for the new size and pitch, plus a matching master setting plug. Your frame, base, and indicator are reused.

    Shop gaging rolls 

  • Replacement or calibration?

    Replace an indicator or setting plug, or send gages in for ISO 17025–accredited calibration. Call 1-888-400-4243.

    Indicators & plugs 
1 3

Which gaging roll type?

TypeWhat it measuresWhen to choose it
Type 3 — Full ProfileFunctional (assembly) diameter.Pitches coarser than 48 TPI; “will it assemble?” checks.
Type 4 — Cone & VeePitch diameter, limited flank contact.Pitch-diameter control across all pitches.
Type 5 — Best WirePitch diameter, best-wire radius.Fine pitches (48 TPI & finer).

Choose your frame

FrameCapacity (in)Capacity (mm)
0.059–.0731.5–1.8
1.073–.0991.8–2.5
2.099–.1642.5–4.2
3.164–.3134.2–7.9
4.313–.5007.9–12.7
5.500–.75012.7–19.0
6.750–1.12519.0–28.5
71.125–1.50028.5–38.1
81.500–1.87538.1–47.6
91.875–2.25047.6–57.1
102.250–2.62557.1–66.7
112.625–3.00066.7–76.2
123.000–3.37576.2–85.7

Each frame covers several standard sizes — confirm the exact fit on the frame product page.

Tri-Roll buying questions

Which frame do I need?

Match your thread's major diameter to a frame's capacity range — see the chart above. Each frame covers several sizes.

Which roll type — 3, 4, or 5?

Type 3 for functional/assembly diameter on pitches coarser than 48 TPI; Type 4 or Type 5 for pitch diameter, with Type 5 best for fine pitches.

Why a master setting plug?

The gage reads variation from a known reference, so it's zeroed against a master setting plug of your thread size before measuring. One plug per thread size.

I already own a Tri-Roll — what do I buy for a new size?

Just a set of gaging rolls for the new size and pitch, plus a matching master setting plug. Your frame, base, and indicator are reused.

Calibration certificates & lead times?

A Long Form Certificate is available on most items, and we offer ISO 17025–accredited calibration. For lead times on made-to-order rolls or plugs, call 1-888-400-4243.