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ACK Asset Management LLC

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13F filer, CIK 1510940, GREENWICH, CT

ACK Asset Management LLC reported $856,327,037 across 21 holdings for the quarter ended 2026-06-30, in a 13F-HR filed 2026-08-13. Its ten largest share positions make up 60.24% of the portfolio.

Filed (acceptance time not in the bulk data set), ingested 13F-HR 0001510940-26-000005

Period
2026-06-30
Reported value
$856M
Holdings
21
Top 10 weight
60.24%
New
7
Sold out
6

Largest buys vs the previous quarter

SecurityShares changeApprox. value
GTXnew+1,500,000$54.3M
BWAnew+600,000$39.8M
DNOWnew+3,000,000$38.9M
STnew+600,000$28.6M
SHLSnew+2,255,000$22.3M

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
MTRNreduced-339,800-$101M
ROGexited-475,000-$51M
NOVTexited-375,000-$44.3M
DXPEexited-260,000-$36.3M
CDNLexited-874,000-$34.7M

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, Q2 2026

Share positions as resolved from 13F-HR 0001510940-26-000005, largest first. % of portfolio is the value over $856,327,037, the sum of the share positions whose value is usable for ratios (method).

SecurityHistorySharesValue% of portfolioChangeLatest eventTimeline
WMSADVANCED DRAIN SYS INC DELQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 345,000 shares; 2025Q3: 390,000 shares; 2025Q4: 390,000 shares; 2026Q1: 390,000 shares; 2026Q2: 390,000 shares 390,000$61.2M7.15%0Timeline
HLIOHELIOS TECHNOLOGIES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 770,000 shares; 2025Q4: 780,378 shares; 2026Q1: 780,378 shares; 2026Q2: 681,000 shares 681,000$60.8M7.1%-99,378Timeline
LFUSLITTELFUSE INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 135,000 shares; 2026Q2: 125,000 shares 125,000$56.9M6.65%-10,000Timeline
JHXJAMES HARDIE INDS PLCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 2,100,000 shares; 2025Q4: 2,100,000 shares; 2026Q1: 2,100,000 shares; 2026Q2: 2,100,000 shares 2,100,000$55M6.42%0Timeline
GTXGARRETT MOTION INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 1,500,000 shares 1,500,000$54.3M6.35%newTimeline
CNMCORE & MAIN INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 900,000 shares; 2025Q4: 900,000 shares; 2026Q1: 900,000 shares; 2026Q2: 1,090,000 shares 1,090,000$52.6M6.14%+190,000Timeline
EXPEAGLE MATLS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 90,000 shares; 2025Q4: 165,000 shares; 2026Q1: 165,000 shares; 2026Q2: 220,000 shares 220,000$49.5M5.78%+55,000Timeline
ATSATS CORPORATIONQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 1,846,196 shares; 2026Q2: 1,500,000 shares 1,500,000$43.2M5.04%-346,196Timeline
ASTEASTEC INDS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 701,500 shares; 2025Q4: 786,500 shares; 2026Q1: 786,500 shares; 2026Q2: 690,276 shares 690,276$42.2M4.93%-96,224Timeline
MTRNMATERION CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: 505,500 shares; 2024Q4: 494,800 shares; 2025Q1: 459,200 shares; 2025Q2: 524,800 shares; 2025Q3: 524,800 shares; 2025Q4: 474,800 shares; 2026Q1: 474,800 shares; 2026Q2: 135,000 shares 135,000$40.1M4.69%-339,800Timeline
BWABORGWARNER INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: 351,400 shares; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 600,000 shares 600,000$39.8M4.65%newTimeline
DNOWDNOW INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 3,000,000 shares 3,000,000$38.9M4.54%newTimeline
MBCMASTERBRAND INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 3,700,000 shares; 2026Q2: 3,700,000 shares 3,700,000$38.1M4.45%0Timeline
SITESITEONE LANDSCAPE SUPPLY INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: 100,000 shares; 2025Q2: 250,000 shares; 2025Q3: 280,000 shares; 2025Q4: 330,000 shares; 2026Q1: 330,000 shares; 2026Q2: 330,000 shares 330,000$37.8M4.41%0Timeline
SWIMLATHAM GROUP INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 5,160,000 shares; 2026Q2: 5,660,000 shares 5,660,000$36.6M4.28%+500,000Timeline
CLFDCLEARFIELD INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: 695,000 shares; 2024Q4: 720,000 shares; 2025Q1: 687,200 shares; 2025Q2: 625,200 shares; 2025Q3: 625,200 shares; 2025Q4: 625,200 shares; 2026Q1: 735,200 shares; 2026Q2: 810,200 shares 810,200$32.2M3.76%+75,000Timeline
STSENSATA TECHNOLOGIES HLDG PLQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 600,000 shares 600,000$28.6M3.34%newTimeline
AERO-SWXAERO-SWXQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 154,851 shares; 2026Q1: 830,000 shares; 2026Q2: 1,082,500 shares 1,082,500$28.5M3.32%+252,500
SHLSSHOALS TECHNOLOGIES GROUP INQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 2,255,000 shares 2,255,000$22.3M2.61%newTimeline
EQPTEQUIPMENTSHARE COM INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 1,064,830 shares 1,064,830$20.9M2.44%newTimeline
MEIMETHODE ELECTRS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: not reported; 2026Q2: 877,500 shares 877,500$16.6M1.94%newTimeline

Sold out in Q2 2026

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

SecurityShares beforeValue beforeType
ROGROGERS CORP475,000$51Mshares
NOVTNOVANTA INC375,000$44.3Mshares
DXPEDXP ENTERPRISES INC260,000$36.3Mshares
CDNLCARDINAL INFRASTRUCTURE GROU874,000$34.7Mshares
GVAGRANITE CONSTR INC250,000$30Mshares
CTSCTS CORP584,000$27.9Mshares

How Q2 2026 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 0001510940-26-000005 base2026-08-13acceptance time not in the bulk data set