Skip to content
Disclosery

ACK Asset Management LLC

Follow

13F filer, CIK 1510940, GREENWICH, CT

ACK Asset Management LLC reported $801,144,828 across 20 holdings for the quarter ended 2026-03-31, in a 13F-HR filed 2026-05-15. Its ten largest share positions make up 61.98% of the portfolio.

Filed (acceptance time not in the bulk data set), ingested 13F-HR 0001510940-26-000004

Period
2026-03-31
Reported value
$801M
Holdings
20
Top 10 weight
61.98%
New
3
Sold out
6

Largest buys vs the previous quarter

SecurityShares changeApprox. value
LFUSnew+135,000$45.8M
CTSnew+584,000$27.9M
SWIMnew+5,160,000$27.7M
AERO-SWXadded+675,149$21.8M
MBCadded+1,400,000$11.6M

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
ENSexited-304,324-$44.7M
ATROexited-597,469-$32.4M
AINexited-600,000-$30.4M
GVAreduced-250,000-$30M
APOGexited-813,000-$29.6M

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, Q1 2026

Share positions as resolved from 13F-HR 0001510940-26-000004, largest first. % of portfolio is the value over $801,144,828, 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; 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; 2026Q1: 474,800 shares 474,800$68.7M8.57%0Timeline
WMSADVANCED DRAIN SYS INC DELQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 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 390,000$53.5M6.68%0Timeline
ATSATS CORPORATIONQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 1,846,196 shares 1,846,196$52.1M6.5%0Timeline
ROGROGERS CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: 590,000 shares; 2024Q4: 580,000 shares; 2025Q1: 517,500 shares; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 436,707 shares; 2026Q1: 475,000 shares 475,000$51M6.36%+38,293Timeline
HLIOHELIOS TECHNOLOGIES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 770,000 shares; 2025Q4: 780,378 shares; 2026Q1: 780,378 shares 780,378$50.5M6.3%0Timeline
LFUSLITTELFUSE INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 135,000 shares 135,000$45.8M5.72%newTimeline
CNMCORE & MAIN INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 900,000 shares; 2025Q4: 900,000 shares; 2026Q1: 900,000 shares 900,000$44.5M5.55%0Timeline
NOVTNOVANTA INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 375,000 shares; 2026Q1: 375,000 shares 375,000$44.3M5.53%0Timeline
SITESITEONE LANDSCAPE SUPPLY INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 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 330,000$43.9M5.48%0Timeline
ASTEASTEC INDS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 701,500 shares; 2025Q4: 786,500 shares; 2026Q1: 786,500 shares 786,500$42.3M5.29%0Timeline
JHXJAMES HARDIE INDS PLCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 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 2,100,000$39.8M4.96%0Timeline
DXPEDXP ENTERPRISES INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: 75,600 shares; 2025Q3: not reported; 2025Q4: 240,000 shares; 2026Q1: 260,000 shares 260,000$36.3M4.53%+20,000Timeline
CDNLCARDINAL INFRASTRUCTURE GROUQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 844,591 shares; 2026Q1: 874,000 shares 874,000$34.7M4.33%+29,409Timeline
EXPEAGLE MATLS INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: 90,000 shares; 2025Q4: 165,000 shares; 2026Q1: 165,000 shares 165,000$31.3M3.9%0Timeline
MBCMASTERBRAND INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 3,700,000 shares 3,700,000$30.7M3.84%+1,400,000Timeline
GVAGRANITE CONSTR INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 250,000 shares 250,000$30M3.74%-250,000Timeline
CTSCTS CORPQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 584,000 shares 584,000$27.9M3.48%newTimeline
SWIMLATHAM GROUP INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: not reported; 2026Q1: 5,160,000 shares 5,160,000$27.7M3.46%newTimeline
AERO-SWXAERO-SWXQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 2024Q2: restricted; 2024Q3: not reported; 2024Q4: not reported; 2025Q1: not reported; 2025Q2: not reported; 2025Q3: not reported; 2025Q4: 154,851 shares; 2026Q1: 830,000 shares 830,000$26.8M3.35%+675,149
CLFDCLEARFIELD INCQuarterly shares; oldest to newest; scale is this security's eight-quarter maximum; 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; 2026Q1: 735,200 shares 735,200$19.5M2.43%+110,000Timeline

Sold out in Q1 2026

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

SecurityShares beforeValue beforeType
ENSENERSYS304,324$44.7Mshares
ATROASTRONICS CORP597,469$32.4Mshares
AINALBANY INTL CORP600,000$30.4Mshares
APOGAPOGEE ENTERPRISES INC813,000$29.6Mshares
ERIIENERGY RECOVERY INC677,251$9.14Mshares
CTOSCUSTOM TRUCK ONE SOURCE INC800,136$4.61Mshares

How Q1 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 0001510940-26-000004 base2026-05-15acceptance time not in the bulk data set