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ACK Asset Management LLC

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13F filer, CIK 1510940, GREENWICH, CT

ACK Asset Management LLC reported $796,756,840 across 23 holdings for the quarter ended 2025-12-31, in a 13F-HR filed 2026-02-13. Its ten largest share positions make up 61.06% of the portfolio.

Filed (acceptance time not in the bulk data set), ingested 13F-HR 0001510940-26-000001

Period
2025-12-31
Reported value
$797M
Holdings
23
Top 10 weight
61.06%
New
6
Sold out
3

Largest buys vs the previous quarter

SecurityShares changeApprox. value
NOVTnew+375,000$44.6M
ROGnew+436,707$40M
DXPEnew+240,000$26.3M
CDNLnew+844,591$20.4M
EXPadded+75,000$15.5M

Ranked by the share change valued at this quarter's implied price (value over shares in the 13F). A position sold out is valued at the previous quarter's price, its last report.

Largest sells vs the previous quarter

SecurityShares changeApprox. value
JBTMexited-350,546-$49.2M
ENSreduced-280,000-$41.1M
ATROreduced-632,531-$34.3M
CTRIexited-1,375,000-$29.1M
NPKIexited-1,576,808-$17.8M

Ranked by the share change valued at this quarter's implied price (value over shares in the 13F). A position sold out is valued at the previous quarter's price, its last report.

Holdings, Q4 2025

Share positions as resolved from 13F-HR 0001510940-26-000001, largest first. % of portfolio is the value over $796,756,840, the sum of the share positions whose value is usable for ratios (method).

SecurityHistorySharesValue% of portfolioChangeLatest eventTimeline
MTRNMATERION CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 505,500 shares; 2024Q4: 494,800 shares; 2025Q1: 459,200 shares; 2025Q2: 524,800 shares; 2025Q3: 524,800 shares; 2025Q4: 474,800 shares 474,800$59M7.41%-50,000Timeline
GVAGRANITE CONSTR INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 825,000 shares; 2024Q4: 284,000 shares; 2025Q1: 190,700 shares; 2025Q2: 545,000 shares; 2025Q3: 545,000 shares; 2025Q4: 500,000 shares 500,000$57.7M7.24%-45,000Timeline
WMSADVANCED DRAIN SYS INC DELQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 345,000 shares; 2025Q3: 390,000 shares; 2025Q4: 390,000 shares 390,000$56.5M7.09%0Timeline
ATSATS CORPORATIONQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 2,255,889 shares; 2024Q4: 2,093,196 shares; 2025Q1: 2,013,196 shares; 2025Q2: 1,846,196 shares; 2025Q3: 1,846,196 shares; 2025Q4: 1,846,196 shares 1,846,196$50.8M6.38%0Timeline
CNMCORE & MAIN INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 900,000 shares; 2025Q4: 900,000 shares 900,000$46.8M5.87%0Timeline
ENSENERSYSQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 715,000 shares; 2024Q4: 671,024 shares; 2025Q1: 624,324 shares; 2025Q2: 584,324 shares; 2025Q3: 584,324 shares; 2025Q4: 304,324 shares 304,324$44.7M5.61%-280,000Timeline
NOVTNOVANTA INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 375,000 shares 375,000$44.6M5.6%newTimeline
JHXJAMES HARDIE INDS PLCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 2,100,000 shares; 2025Q4: 2,100,000 shares 2,100,000$43.6M5.47%0Timeline
HLIOHELIOS TECHNOLOGIES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 770,000 shares; 2025Q4: 780,378 shares 780,378$41.7M5.24%+10,378Timeline
SITESITEONE LANDSCAPE SUPPLY INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: 100,000 shares; 2025Q2: 250,000 shares; 2025Q3: 280,000 shares; 2025Q4: 330,000 shares 330,000$41.1M5.16%+50,000Timeline
ROGROGERS CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 590,000 shares; 2024Q4: 580,000 shares; 2025Q1: 517,500 shares; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 436,707 shares 436,707$40M5.02%newTimeline
EXPEAGLE MATLS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 90,000 shares; 2025Q4: 165,000 shares 165,000$34.1M4.28%+75,000Timeline
ASTEASTEC INDS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 701,500 shares; 2025Q4: 786,500 shares 786,500$34.1M4.28%+85,000Timeline
ATROASTRONICS CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 2,060,000 shares; 2024Q4: 2,060,000 shares; 2025Q1: 2,060,000 shares; 2025Q2: 2,060,000 shares; 2025Q3: 1,230,000 shares; 2025Q4: 597,469 shares 597,469$32.4M4.07%-632,531Timeline
AINALBANY INTL CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 585,000 shares; 2025Q3: 760,000 shares; 2025Q4: 600,000 shares 600,000$30.4M3.82%-160,000Timeline
APOGAPOGEE ENTERPRISES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 708,000 shares; 2025Q4: 813,000 shares 813,000$29.6M3.72%+105,000Timeline
DXPEDXP ENTERPRISES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 75,600 shares; 2025Q3: not reported; 2025Q4: 240,000 shares 240,000$26.3M3.31%newTimeline
MBCMASTERBRAND INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 650,000 shares; 2024Q4: 1,475,000 shares; 2025Q1: 1,302,500 shares; 2025Q2: not reported; 2025Q3: 2,300,000 shares; 2025Q4: 2,300,000 shares 2,300,000$25.4M3.19%0Timeline
CDNLCARDINAL INFRASTRUCTURE GROUQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 844,591 shares 844,591$20.4M2.56%newTimeline
CLFDCLEARFIELD INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: 695,000 shares; 2024Q4: 720,000 shares; 2025Q1: 687,200 shares; 2025Q2: 625,200 shares; 2025Q3: 625,200 shares; 2025Q4: 625,200 shares 625,200$18.2M2.29%0Timeline
ERIIENERGY RECOVERY INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 677,251 shares 677,251$9.14M1.15%newTimeline
AERO-SWXAERO-SWXQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 154,851 shares 154,851$5.53M0.69%new
CTOSCUSTOM TRUCK ONE SOURCE INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q1: restricted; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 1,875,000 shares; 2025Q3: 1,925,000 shares; 2025Q4: 800,136 shares 800,136$4.61M0.58%-1,124,864Timeline

Sold out in Q4 2025

Positions in the previous quarter's report that this quarter's report no longer lists.

SecurityShares beforeValue beforeType
JBTMJBT MAREL CORPORATION350,546$49.2Mshares
CTRICENTURI HOLDINGS INC1,375,000$29.1Mshares
NPKINPK INTERNATIONAL INC1,576,808$17.8Mshares

How Q4 2025 was built

Available 13F filings of this filer for the quarter and their roles: the base report is the latest original or restatement, NEW HOLDINGS amendments filed after it are added (method).

FilingRoleAmendmentFiledAcceptedIngested
13F-HR 0001510940-26-000001 base2026-02-13acceptance time not in the bulk data set