A standard 300x300 mm 718 (P20+Ni) two-plate mold base from a Chinese mold base supplier landed in the $1,200-$1,800 FOB band in mid-2026, while the same frame in H13 (1.2344) with a pre-hardened 30-33 HRC cavity retainer moved into the $2,400-$3,600 band [S1][S2].
For injection tooling, a mold base is the pre-engineered steel frame (A/B plates, support pillars, guide bushings, sprue bushing, return pins, ejector plate) into which cavities and cores are cut; for die casting, the equivalent is a die set sized to the machine platen, typically S50C or S55C body with H13 inserts. As covered in the Mold Base Buying Guide 2026, the frame usually represents 25-40% of total tool cost on a multi-cavity plastic mold, and 15-25% on a die casting die.
What a 2026 mold base price actually includes
A quoted mold base price in 2026 typically covers the A-plate, B-plate, support plate, cavity retainer, core retainer, four guide pillars (SF-1 self-lubricating or SUJ2 bearing steel), four guide bushings, sprue bushing, locating ring, support pillars, ejector pins, return springs, and a standard LKM or HASCO datuming scheme [S1][S2].
What it does NOT include by default on a Chinese supplier quote: CNC cavity machining, EDM, polishing past SPI-A3, heat treatment above 30-33 HRC, fitting to a customer-supplied drawing, or hot-runner manifolds — those line items typically add 30-120% on top of the base frame price, and ignoring them is the single most common budgeting error for first-time tooling buyers [S1]. YHY's catalog breaks the frame out of the value-added machining, which is the cleaner way to read a mold base RFQ [S1].
The four cost levers that move the number
1) Steel grade. S50C/S55C (1.1730) carbon steel at 175-220 HB is the cheapest frame material and is adequate for short-run plastic tools under 100k shots; the upgrade to P20 (1.2311, 28-32 HRC) typically adds 20-35% to the frame price, while 718 / P20+Ni (1.2738, 30-33 HRC pre-hardened) adds 35-55%, and H13 (1.2344, 48-52 HRC after heat treat) for die casting and high-wear plastic tooling adds 60-110% [S1][S2].
2) Frame size and plate thickness. A 200x200 mm frame with 30 mm plates costs roughly 35-45% of a 500x500 mm frame with 60 mm plates, because the steel tonnage and CNC machining hours scale with the cube of plate dimension rather than linearly. Plate thickness below 25 mm or above 80 mm triggers a custom surcharge on most Chinese mold base suppliers [S1].
3) Tolerance class. Standard frame datuming at ±0.03 mm is the catalog baseline; tightening to ±0.01 mm on guide pillar bores for high-cavitation tools adds 10-20%, and going to ±0.005 mm with matched-bushing pairs adds 25-40% [S2]. HASCO and DME standard tolerances are tighter than generic LKM copies by 20-30% on the same steel grade, and the brand premium shows up directly in the mold base price.
4) Cavity count and fit. A 1-cavity frame is roughly 70-80% of a 2-cavity frame cost (the frame itself barely changes; the cavity retainer work doubles). A 4-cavity frame typically runs 1.6-1.9x a 2-cavity, and 8-cavity 1.4-1.7x a 4-cavity — economies of scale diminish past 4 cavities because of runner balancing and gate machining complexity. For die casting, the Mold Base vs Die Casting Die comparison shows a 2-cavity H13 die set landing 1.8-2.4x the equivalent 2-cavity plastic mold base because of the heavier wall section and shot sleeve integration.
2026 price bands by frame class
Standard LKM-type 718 frame, 250-350 mm, 2-cavity-ready, FOB Shenzhen: $1,200-$1,800 for S50C, $1,800-$2,800 for P20, $2,400-$3,600 for 718 (1.2738) pre-hardened [S1][S2].
Mid-class HASCO / DME equivalent, 350-500 mm, 4-cavity-ready, with pre-hardened cavity retainer and SUJ2 guide pillars: $3,800-$6,500 in P20, $5,200-$8,800 in 718, $7,500-$13,000 in H13 [S1].
Large-format frame 500-800 mm, 8-cavity-ready, custom plate thickness, hot-runner manifold interface machined (manifold not included): $9,000-$14,000 in P20, $11,000-$18,000 in 718, $14,000-$25,000+ in H13 with full heat treat and EDM datuming [S1][S2]. Die casting die sets in the same size class land 20-40% above the equivalent plastic mold base because of S50C body + H13 insert construction and waterline integration.
For context on what surrounds a mold base in a complete tool, the Die Casting Die Selection Checklist lays out the cavity, ejector, cooling and lubrication sub-systems that get quoted separately from the base frame.
Comparison: frame material vs cost vs application fit
S50C / 1.1730: lowest cost, 175-220 HB as-supplied, suits prototype plastic tools and runs under 100k shots. Not weldable for repair on production tools [S1].
P20 / 1.2311: mid-cost at +20-35% over S50C, 28-32 HRC pre-hardened, the workhorse for plastic injection tools up to 500k-1M shots, weldable with proper procedure. The default choice for consumer-product plastic tooling in 2026 [S1][S2].
718 / P20+Ni / 1.2738: premium at +35-55% over S50C, 30-33 HRC pre-hardened, nickel content gives through-thickness hardness uniformity on thick plates, the standard for large plastic tools over 500 mm frame size and for tools requiring mirror polish to SPI-A1 [S1].
H13 / 1.2344: highest at +60-110% over S50C, supplied annealed and heat-treated to 48-52 HRC, mandatory for die casting dies, high-pressure die casting, and any plastic tool running glass-filled engineering resins above 30% filler. The die casting and zinc / magnesium die casting industries run almost exclusively H13 inserts in an S50C or S55C frame, which is why the Zinc Die Casting Machine Buying Guide and the Magnesium Die Casting Machine spec levers piece both reference H13 die sets rather than pre-hardened plastic grades [S1][S2].
Hidden cost multipliers buyers miss
Heat treatment. Quench-and-temper to 48-52 HRC on H13 adds 8-12% to the frame line and 1-2 weeks of lead time; vacuum heat treatment for tools that will see mirror polishing adds another 5-7% but cuts post-polish sink marks on cosmetic parts [S1].
Guide pillar / bushing spec. SUJ2 (1.3505, 100Cr6 equivalent) is the standard bearing-steel pair; SF-1 bronze-impregnated self-lubricating bushings run $8-$15 each versus $3-$5 for the SUJ2 pair, but eliminate the need for grease lubrication on clean-room medical or food tools. Hardness on the guide pillars above 58 HRC adds $20-$40 per set but is mandatory for high-cavitation tools above 4 cavities [S1][S2].
Datuming and standard. LKM is the Chinese de-facto standard and the cheapest because of local tooling-board availability. HASCO and DME standards add 15-25% to the frame price on identical steel, but the components are interchangeable with European-supplied hot-runner manifolds and ejector systems, which is the real reason most export-oriented mold shops pay the premium [S2].
Lead time. Standard 718 frames in catalog sizes ship in 10-15 working days from Shenzhen-area suppliers in mid-2026; non-standard sizes or H13 with heat treat run 20-30 working days; rush orders under 10 working days carry a 20-40% expedite surcharge on the base frame price [S1][S2].
Where a Chinese mold base supplier quote does and does not beat domestic
On a 718 frame, 350x400 mm, 2-cavity-ready, FOB versus DDP North America or Western Europe, the China-supplied frame landed 40-55% below a comparable U.S. or German shop quote in mid-2026, with the gap narrowing to 25-35% on H13 die casting die sets because of the heavier steel and tighter heat-treat control [S1][S2].
The gap reverses on small format 200x200 mm S50C prototype frames: shipping cost, import duty, and the supplier minimum order value (typically $800-$1,500 on Chinese mold base suppliers) can wipe out the unit-cost advantage on prototypes, and a local CNC shop building the frame from datumed stock plate often wins on lead time and total cost for sub-300 mm frames under 5 units [S1].
Standardization matters. YHY and COMEKIN both publish catalog LKM-type frames in 100 mm size steps from 150x150 to 600x600 mm; custom sizes outside those steps typically carry a 15-25% surcharge and a 5-10 day lead time penalty versus catalog [S1][S2].
What the mold base price does not tell you about total tool cost
The base frame is roughly the third-largest line on a complete plastic injection mold quote, after cavity machining + EDM and the hot-runner system (where fitted). On a typical 4-cavity consumer product mold with a hot runner, expect the base frame to be 18-28% of the total; on a 1-cavity prototype tool with a cold runner, the base frame can be 35-50% of the total [S1][S2].
For sand-casting pattern frames and related casting tooling, the cost profile is different — patterns are typically wood, aluminum, or resin rather than hardened tool steel, and the sand casting mold price guide breaks that cost stack out separately. Crossed-roller and linear guide systems used in the die set's ejector and slide mechanisms are spec'd to a different cost band entirely, covered in the linear guide and crossed-roller guide encyclopedia entries.
Trackable signals to watch for Q4 2026: 718 / 1.2738 plate steel spot price in Foshan and Dongguan warehouses (the single biggest input cost for a mid-class mold base), and Chinese mold base supplier published lead times — both moved noticeably through H1 2026 and drive the next round of frame-price revisions [S1][S2].