It is 9:18 a.m. inside a contract analytical lab on the second floor of a Research Triangle Park biotech incubator. The receiving bench has thirty-six 8 oz wide-mouth PP jars staged in a transfer rack, each one holding a homogenized soil split bound for ICP-MS digestion that afternoon. The lab tech needs every jar capped, threaded down to a defined torque, and walked into a fume hood within four minutes — because the chain-of-custody clock starts the moment the lid touches the finish, and an audit-grade COC log will not tolerate a six-minute gap between aliquot and seal. The reason that rack moves on schedule and not on tomorrow's schedule is that the 70-400 white PP smooth cap threads on cleanly, lands flush, and accepts a torque-meter check the same way every time. That is what this cap is engineered to do.
What the 3303C19WHT Actually Is
A 70-400 continuous-thread white polypropylene cap with a fully smooth top panel and smooth side skirt — no knurls, no ribs, no decoration features that would interfere with a torque-meter ring, a label wrap, or a clean hand-tighten cycle. The 70-400 designation is the SPI thread spec: 70 mm nominal cap inside diameter on a 0.400 in finish height with a single continuous thread pitch matching any standard 70-400 jar shoulder. PP — polypropylene resin, FDA-permitted for food contact under 21 CFR 177.1520, autoclave-tolerant up to 250 °F, chemically inert against most aqueous reagents and many polar solvents. Case pack 760 caps per master case. Listed at $0.29 per cap (jar sold separately, freight quoted separately to your delivery ZIP via the freight estimator at /freight-cost-estimator/ or by phone). BPA was not intentionally used in the manufacture of this cap.
Why 70-400 Is the Wide-Mouth Workhorse
The 70-400 finish lands in the middle of the wide-mouth jar program — wider than the 53-400 and 63-400 cosmetic-jar sizes, narrower than the 89-400 and 110-400 institutional jars. That puts it on the receiving end of jars in the 6 oz to 32 oz volume class: 8 oz wide-mouth PP straight-sided jars, 16 oz PET wide-mouth food jars, 32 oz HDPE sample containers, and the standard 16 oz amber glass jars that analytical labs and environmental testing services use for soil, sediment, and water-sample submission. One cap SKU, one torque profile, one inventory line — across a jar program that can otherwise need four or five separate closure SKUs.
Smooth Versus Ribbed Surface
Ribbed caps are the volume default on consumer goods because the ribs give a thumb the grip to break a tight seal one-handed at the kitchen counter. A smooth cap trades that grip for three things that matter in a regulated or production setting. First, the smooth top panel takes a flat round label or hot-stamped lot code without the rib-shadow that distorts a barcode scan. Second, the smooth side skirt seats cleanly in a torque-cap chuck on an automated bench or in-line capper — ribs can catch in the chuck and skew the applied torque. Third, the smooth profile drops cleanly into a tabletop induction-seal foil applicator without the rib-cavity that traps stray foil scraps. For a lab tech applying a calibrated 12 in-lb torque or a co-packer running a benchtop capper at 200 caps per hour, smooth is the right surface.
Material — PP Specifics That Matter for Lab Use
Polypropylene is the standard resin for laboratory sample-handling because of three properties that LDPE and HDPE do not match. Working temperature ceiling is 250 °F (121 °C) — high enough to autoclave the empty cap on a 121 °C / 15 psi gravity-displacement cycle for sterile sample collection. Chemical resistance: PP holds against most dilute mineral acids, common alkalis, alcohols, glycols, and the routine reagent matrix in a wet chemistry or environmental lab. Limitations: PP is attacked by aromatic and chlorinated hydrocarbons (toluene, benzene, dichloromethane, chloroform) — for those streams switch to an FEP- or PTFE-lined closure. Specific gravity 0.90, so a case of 760 caps weighs roughly 6.5 lb net, freight-friendly for parcel small-quantity orders.
Liners and Induction Seals
The 3303C19WHT is supplied as an unlined shell. For a finished seal pick the liner that matches the application: pulp + foil for tamper-evident bulk powder, F-217 polyethylene foam for low-cost dry-product seal, plain PE-foam for cosmetic creams, or an induction-seal heat-activated foil for any liquid or semi-liquid that needs a leak-proof primary seal during freight. The 70 mm liner inside diameter accepts any of the standard 70 mm liner-stock cut by Selig, Tri-Seal, or in-house die-cut converters. Call us for liner-pack pricing if the project needs sealed caps shipped together.
Order Math for a Research Lab or Co-Packer
760 caps in a master case at $0.29 per cap puts the case landed cost near $220 before freight. That is roughly two months of cap inventory for a mid-sized analytical lab running 200 sample jars per week, or one month for a contract environmental services group processing 800 jars per week through a 70-400 program. For a private-label e-commerce brand bottling skincare or hair-care into 8 oz wide-mouth jars, a single 760-count case covers the first 600-700 retail units plus QC reject overhead. For ramp scenarios — a brand going from 600 units a week to 4,000 — the caps stock at the manufacturer warehouse for next-business-day cut and 3-5 day LTL freight, which means the cap is not the constraint on the brand's growth.
Decoration and Labeling
The flat smooth top panel is the largest decoration real estate of any 70 mm cap surface — roughly a 2.4 in diameter circle of clean white PP that takes a flexo round label, a hot-foil stamp, a pad-print logo, or a direct-thermal lot/date code from a Markem-Imaje or Videojet inline coder. The smooth side skirt takes a wraparound shrink-band tamper-evident seal up to 18 mm tall. Direct silk-screen printing on the cap top is available for production runs of 10,000 per color. Call for decoration setup and per-piece pricing.
Order a Case-Pack Quote
Call 866-418-1777 to confirm 760-count master-case quantity, freight class to your delivery ZIP, and lead time on the 3303C19WHT from current warehouse inventory. The same call covers matching 70-400 jar inventory if the project needs jars and caps shipped together on one BOL.
FAQ
What jar finishes does the 3303C19WHT fit?
Any 70-400 continuous-thread jar finish. The 70-400 SPI spec is 70 mm nominal inside diameter on a 0.400 in finish height with a single continuous thread pitch. That covers a wide-mouth program of 8 oz to 32 oz PP, HDPE, PET, and amber-glass jars. Confirm your jar finish callout matches '70-400' on the supplier spec sheet before ordering.
Why pick a smooth cap instead of a ribbed cap?
Smooth caps seat cleanly in a torque-cap chuck, take a flat round label or barcode without rib-shadow distortion, and drop into a tabletop induction-seal applicator without trapping stray foil. Ribbed caps are the volume default for consumer hand-grip, but a regulated or automated production line wants the smooth surface for repeatable torque and clean decoration.
Is the PP resin autoclave-tolerant for sterile sample collection?
Yes. Polypropylene holds geometry on a standard 121 °C / 15 psi gravity-displacement autoclave cycle. For sterile sample collection a lab can autoclave the empty cap and jar separately, transfer aseptically, and seal. Working temperature ceiling is 250 °F (121 °C). For continuous service above that temperature pick a different resin.
Is the cap supplied with a liner?
No — the 3303C19WHT ships as an unlined shell. Pick the matching 70 mm liner separately based on the stream: pulp + foil for dry tamper-evident, F-217 PE-foam for low-cost dry seal, plain PE-foam for cosmetic cream, or induction-seal heat-activated foil for liquid leak-proof primary seal. Call 866-418-1777 for liner-pack pricing or to ship lined caps as a single line.
What is the case pack quantity and minimum order?
760 caps per master case. Minimum order is one cap (MOQ 1) for sample-evaluation orders. Production-grade volumes ship in full 760-count master cases. For multi-case orders we can ship full pallets of caps at LTL freight rates — call 866-418-1777 for full-pallet pricing and lead time.
How is freight quoted on this cap?
List price is per-unit. LTL freight is quoted separately to your delivery ZIP through our freight estimator at /freight-cost-estimator/ or by phone at 866-418-1777. Pallet rate, residential delivery surcharge, and lift-gate are quoted at the same time. We do not bundle freight into the cap list price.
Is this cap FDA-compliant for food contact?
Yes. Polypropylene is an FDA-permitted food-contact resin under 21 CFR 177.1520 — the standard regulation covering olefin polymers for food packaging. BPA was not intentionally used in the manufacture of this cap. For specific regulated content (infant formula, OTC drug, dietary supplement) confirm full compliance documentation needs with your formulator and our team before scaling production.
Sources cited: FDA 21 CFR 177.1520 (polypropylene food-contact regulation), SPI thread finish standard 70-400 (continuous-thread cap spec), OneSource Plastics 3303C19WHT technical specification
