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Linen Phenolic Specifications: Sizes, Tolerances & Standards

Linen phenolic stock is manufactured to NEMA LI 1 dimensional and property standards and is also referenced in MIL-I-24768 (MIL-SPEC) procurement. Both NEMA grades — L and LE — are available in three forms: flat sheet, round rod, and tube. This page covers standard stock sizes, thickness and diameter tolerances, flatness requirements, and ordering considerations for each form.

At a glance:

  • Sheet: standard master size 36 × 48 in; nominal thickness from 1/32 in to 4 in
  • Rod: ¼ in to 6 in diameter; standard lengths 4 ft or 6 ft
  • Tube: range of wall thicknesses; OD from approx. ½ in to 6 in
  • Thickness tolerance on sheet: ±5–10 % per NEMA LI 1 (tighter grades available)
  • Diameter tolerance on rod: ±0.010 in to ±0.020 in (as-laminated); finish-ground to ±0.001 in on request
  • Color: natural light tan; no standard pigmented grades

Governing Standards

Linen phenolic is manufactured and tested to:

  • NEMA LI 1 — Industry standard for industrial laminated thermosetting products. Defines mechanical and electrical property minima by grade designation (L, LE) and form (sheet, rod, tube).
  • ASTM D709 — Standard specification for laminated thermosetting materials; referenced alongside NEMA LI 1 for dimensional tolerances.
  • MIL-I-24768 — U.S. military procurement specification for laminated thermosetting insulating materials. Grade L maps to Type FBM; grade LE maps to Type FBME.
  • ASTM D638, D790, D695, D149, D150, D257 — Individual test methods referenced within NEMA LI 1 for property verification.

When ordering for defense or aerospace procurement, specify the MIL-I-24768 type designation and request a Certificate of Conformance (C of C) from the manufacturer.

Sheet Specifications

Standard Sheet Sizes

Linen phenolic flat sheet is produced in nominal master-panel dimensions. The most common master size is 36 in × 48 in, though some manufacturers offer 48 × 48 and 48 × 96 panels in heavier gauges. Cut-to-size service is standard; minimum practical cut size depends on thickness and gauge.

Thickness Range

NEMA LI 1 tolerances are one-sided positive — sheets are nominally at or above the stated thickness. For applications requiring a tight thickness envelope (e.g., shim plates in optical assemblies), request ground sheet or specify a tighter tolerance in your purchase order. Grinding to ±0.001 in is available at additional cost.

Flatness

NEMA LI 1 specifies flatness as a bow-per-foot value that varies with thickness. Thin sheet (under 1/8 in) is inherently less flat than thick sheet and may require support fixturing during machining. Standard linen phenolic sheet is not guaranteed to remain flat after machining that removes material asymmetrically — stress relief cuts and balanced material removal are required for precision flat parts.

Rod Specifications

Diameter Range

Round rod is the preferred starting form for turned precision parts — bushings, gear blanks, sleeves, and standoffs. Linen phenolic rod is continuously pultrusion-laminated or mandrel-wound, producing a circular cross-section with concentric lamination rings.

Standard rod lengths are 6 ft for diameters up to 3 in and 4 ft for larger diameters. Shorter cut lengths are available by request.

Finish-Ground Rod

As-laminated rod surfaces are not precision surfaces — they show mold-release residue and minor surface porosity. For direct use as a bearing surface, specify centerless-ground rod, which achieves:

  • Outside diameter: ±0.001 in
  • Surface finish: 32–63 µin Ra
  • Straightness: 0.010 in per foot maximum

Centerless-ground linen LE rod is stocked in the most common diameters (1/4 in through 2 in); larger sizes are ground on request.

Tube Specifications

Wall Thickness and OD Range

Linen phenolic tube is manufactured by mandrel winding or hot-press tube lamination. Standard tube stock covers:

  • OD range: approximately 3/4 in to 6 in
  • Wall thickness: 1/16 in to 1/2 in (standard); custom walls available
  • Length: 3 ft or 6 ft standard

Tube is advantageous for hollow-cylinder parts — sleeve bearings, insulating sleeves, bobbin cores — because the pre-formed bore eliminates most of the axial boring operation, saving cycle time and material.

Custom wall thicknesses and non-standard OD/ID combinations are available with extended lead times. Provide target OD, wall, and length when requesting a quote.

Dimensional Tolerance Comparison: Linen vs. Cotton Phenolic

Linen phenolic's finer weave yields a slight advantage in dimensional consistency over cotton-reinforced grades from the same manufacturer:

This difference becomes significant when machining toleranced parts directly from stock without a facing or turning operation. Linen phenolic starts closer to nominal, reducing setup time.

Ordering and Lead Time

Standard sheet, rod, and tube in NEMA L and LE are stocked for quick-turn delivery. Custom cuts, finish-ground rod, and non-standard tube dimensions typically require 5–15 business days depending on quantity and form. For MIL-I-24768 procurement with C of C, allow additional lead time for documentation.

For detailed stock availability and current pricing, visit the linen phenolic line card page.

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